1007_素数对猜想 (20)

#include<stdio.h>#include<math.h>int isprime(int n){int i;for(i=2;i<=sqrt(n);i++)if(n%i==0) return 0;return 1;}int main(){int n,i,sum,t;while(~scanf("%d",&n)){if(n>=100000||n<1) continue;sum=0;t=3;for(i=4;i<=n;i++)if(isprime(i)){if((i-t)==2) sum++;t=i;}printf("%d\n",sum);}return 0;}