PAT1007 #include<iostream> using namespace std; int even(int n) { for (int i = 2; i *i<= n; i++) { if (n % i == 0) { return 0; } } return 1; } int main() { int N; cin >> N; int num = 0; for (int i = 5; i <= N; i++) { if (even(i - 2) && even(i))num++; } cout << num << endl; }