50 lines
1.3 KiB
C++
50 lines
1.3 KiB
C++
#include <map>
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#include <set>
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#include <stack>
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#include <queue>
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#include <cmath>
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#include <ctime>
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#include <vector>
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#include <cstdio>
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#include <cctype>
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#include <cstring>
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#include <cstdlib>
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#include <iostream>
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#include <algorithm>
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using namespace std;
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#define INF ((LL)100000000000000000)
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#define inf (-((LL)1<<40))
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#define lson k<<1, L, mid
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#define rson k<<1|1, mid+1, R
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#define mem0(a) memset(a,0,sizeof(a))
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#define mem1(a) memset(a,-1,sizeof(a))
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#define mem(a, b) memset(a, b, sizeof(a))
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template<class T> T CMP_MIN(T a, T b) { return a < b; }
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template<class T> T CMP_MAX(T a, T b) { return a > b; }
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template<class T> T MAX(T a, T b) { return a > b ? a : b; }
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template<class T> T MIN(T a, T b) { return a < b ? a : b; }
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template<class T> T GCD(T a, T b) { return b ? GCD(b, a%b) : a; }
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template<class T> T LCM(T a, T b) { return a / GCD(a,b) * b; }
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typedef long long LL;
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const int MAXN = 255;
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const int MAXM = 110000;
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const double eps = 1e-12;
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double t[30];
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int main()
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{
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double p;
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while(~scanf("%lf", &p))
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{
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t[0] = 0;
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t[1] = 1 / p;
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t[2] = 1 / p + 1 / p / p;
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for(int i=3;i<=20;i++)
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{
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t[i] = 1 / p * t[i-1] + 1 / p - (1-p) / p * t[i-3];
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}
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double ans = 2 *t[19] + t[20] - t[19];
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printf("%lf\n", ans);
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}
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return 0;
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}
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