#include<fstream>

using namespace std;

ifstream f("ciur.in");
ofstream g("ciur.out");

const int Nmax = 2000005;

bool prim[Nmax];
int nr, n;

void solve(){

    f >> n;

    for(int i = 2; i <= n; i++)
        if(!prim[i]){

        ++nr;
        for(int j = i + i; j <= n; j += i)
            prim[j] = 1;
    }

    g << nr;
}

int main(){

    solve();

    return 0;
}