#include <bits/stdc++.h>
using namespace std;
int main(){
    ifstream fin("ciur.in");
    ofstream fout("ciur.out");
    int N;
    fin>>N;
    vector<bool> composite(N + 1);
    int cnt = 0;
    for (int p = 2; p <= N; ++p) {
        if (!composite[p]) {
            cnt++;
            if (1LL * p * p <= N) {
                for (long long multiple = 1LL * p * p; multiple <= N; multiple += p) {
                    composite[multiple] = true;
                }
            }
        }
    }
    fout<<cnt;
    return 0;
}