#include<iostream>
using namespace std;
int main()
{
int m;
cin >> m;
int a[10000] = { 0 };
for (int i = 0; i < m; i++)a[i] = 1;
int i = 2;
while (i<m)
{
for (int j = 2; (j*i) < m; j++)a[j*i] = 0;
i++;
while (a[i] == 0)i++;
}
int tag1=2;
int cnt = 0;
for (int i = 3; i < m; i++)if (a[i]) {
if ((i-tag1)==2)cnt++;
tag1 = i;
}
cout << cnt;
}
少了#include
using namespace std;
应该是复制提交的时候的失误