#include <iostream>
#include<fstream>

using namespace std;

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

bool v[2000000];

int main()
{
    int n, i, j, c=0;
    in >> n;

    for(i=2; i<=n; i++){
        if(v[i]==0){
            c++;
            for(j=i; j<=n; j+=i){
                v[j] = 1;
            }
        }
    }

    out << c;

    return 0;
}