#include <iostream>
#include<fstream>
#include<cmath>
using namespace std;

ifstream in("ciur.in");
ofstream out("ciur.out");
int main()
{

    int N,C = 0;
    bool *v;
    in>>N;
    v = new bool[N];

    for(int i = 0;i<N;i++){
        v[i] = 1;
    }
    v[0] = 0;
    v[1] = 0;

    for(int i = 2;i<N;i++){
        if(v[i]){
                C++;
            for(int j = 2*i;j<=N;j+=i){
                v[j] = 0;
            }
        }
    }


out<<C;

    return 0;
}