34 lines
600 B
C++
34 lines
600 B
C++
#include<cstdio>
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#include<cstring>
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#include<iostream>
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using namespace std;
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const int maxn=1000011;
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int n;
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long long ans[maxn],phi[maxn];
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void Phi(int n)
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{
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phi[1]=1;
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for(int i=2;i<=n;i++)
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if(!phi[i])
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for(int j=i;j<=n;j+=i)
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{
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if(!phi[j])
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phi[j]=j;
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phi[j]=phi[j]/i*(i-1);
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}
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}
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int main()
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{
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Phi(maxn-1);
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ans[1]=2;
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ans[2]=3;
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for(int i=3;i<maxn;i++)
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ans[i]=ans[i-1]+phi[i];
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while(scanf("%d",&n)!=EOF)
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{
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long long s=(ans[n]-2)*2+3;
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printf("%I64d\n",s);
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}
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return 0;
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}
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