#include <bits/stdc++.h>

using namespace std;
const int Nmax = 2000005;
bitset<Nmax> ciur;


int main()
{
    freopen("ciur.in", "r", stdin);
    freopen("ciur.out", "w", stdout);

    int N;
    scanf("%d", &N);
    int cnt = 1;
    for(int i = 3; i <= N; i += 2)
        if(ciur[i] == 0){
            ++cnt;
            for(int j = 3; i * j <= N; j += 2)
                ciur[i * j] = true;
        }
    cout << cnt;


    return 0;
}