#include <fstream>
#define nmax 2000001

using namespace std;
ifstream f("ciur.in");
ofstream g("ciur.out");
int N, contor;
bool v[nmax];
int main()
{int i, numar, j = 2;
    f>>N;
    for(i = 2; i <= N; ++i){
        if(v[i] == 0){
                numar = i;
            while(numar * j <= N){
                v[numar * j] = 1;
                ++j;
            }
            j = 2;
        }
    }
    for(i = 2 ; i <= N ; ++i){
        if(v[i] == 0) ++contor;
        //g<< v[i]<<' ';
    }
    g<<contor<<'\n';
    return 0;
}