#include <iostream>
#include <fstream>

using namespace std;

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

bool v[2000001];

int main()
{
    int n;
    fin>>n;

    int cnt = 0;
    for(int i = 2; i * i <= n; i++){
        if(v[i] == 0){
            for(int j = 2; j <= n / i; j++){
                v[i * j] = 1;
            }
        }

    }

    for(int i = 2; i <= n; i++){
        if(v[i] == 0){
            cnt++;
        }
    }

    fout<<cnt;

    return 0;
}