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#include <bits/stdc++.h>
using namespace std;
//判断是不是质数
bool isPrime(int n) { //最快的方法
if (n < 2) return false;
if (n == 2 || n == 3) return true;
if (n % 6 != 1 && n % 6 != 5) return false;
for (int i = 5; i <= floor(sqrt(n)); i += 6)
if (n % i == 0 || n % (i + 2) == 0)
return false;
return true;
}
int main() {
int n;
cin >> n;
int count = 0;
for (int i = 2; i <= n; ++i) {
if (isPrime(i))count++;
}
cout << count << endl;
return 0;
}