#include <bits/stdc++.h>

using namespace std;

bool notPrime[2000002];

int main() {
    ifstream fin("ciur.in");
    ofstream fout("ciur.out");
    int n, answer = 0;
    fin >> n;
    notPrime[0] = notPrime[1] = 1;
    for (int i = 2; i <= n; ++i) {
        if (!notPrime[i])
        {
            answer += 1;
            for (int j = i + i; j <= n; j += i) {
                notPrime[j] = 1;
            }
        }
    }
    fout << answer;
    return 0;
}