#include <fstream>

using namespace std;

int n,i,ap,j;

char v[2000002];

ifstream fin ("ciur.in");

ofstream fout ("ciur.out");

int main (){

    fin>>n;
    ap = 0;
    for (i=2;i<=n;i++){
        if (v[i] == 0){
            for (j=i+i;j<=n;j+=i)
                v[j] = 1;
            ap++;
        }
    }
    fout<<ap;

    return 0;
}