26 lines
396 B
C++
26 lines
396 B
C++
#include<string.h>
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#include<cstdio>
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#include<iostream>
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#include<algorithm>
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const int MAX=31;
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int s[MAX];
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using namespace std;
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int main()
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{
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int i,n;
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s[0]=1;
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s[2]=3;
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for(i=4;i<MAX;i+=2)
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{
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s[i]=4*s[i-2]-s[i-4];
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}
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while(cin>>n,n>=0)
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{
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if(n&1)
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cout<<0<<endl;
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else
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cout<<s[n]<<endl;
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}
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return 0;
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}
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