#include <iostream>
#include <fstream>
using namespace std;
ifstream in("ciur.in");
ofstream out("ciur.out");
bool prim[2000010];
int cnt, N;
int main()
{
    in >> N;
    prim[0] = prim[1] = 1;
    for(int i = 2;i <= N;i++){
    if(prim[i] == 0){
            cnt++;
        for(int j = 2;j * i <= N;j++)
            prim[j * i] = 1;
        }
    }
    out << cnt;
    return 0;
}