#include <fstream>
#define DMAX 2000004
using namespace std;

ifstream fin("ciur.in");
ofstream fout("ciur.out");


int n;
bool prim[DMAX];
int nr;

int main(){

    fin>>n;

    int i, j;
    for(i = 2; i <= n; ++i) prim[i] = 1;

    for(i = 2; i * i <= n; ++i)
        if(prim[i]){
            for(j = i; j<=n / i; ++j){
                prim[i*j] = 0;
            }
        }

    for(i = 2; i<= n; ++i)
        if(prim[i]) ++nr;
    fout<<nr;



    return 0;
}