#include <bits/stdc++.h>
using namespace std;

int n, nmax = 2000001;
vector<bool> a(nmax);

int main(){
    ifstream cin("ciur.in");
    ofstream cout("ciur.out");
    cin >> n;
    for(int i = 2; i * i <= nmax; ++i)
        if(!a[i])
            for(int j = 2; j <= nmax / i; ++j)
                a[i * j] = 1;

    int ans = 0;
    for(int i = 2; i <= n; ++i)
        if(!a[i])
            ++ans;
    cout << ans;
}