#include <iostream>
#include <fstream>
using namespace std;
ifstream in("ciur.in");
ofstream out("ciur.out");
const int dim = 2000001;

bool c[dim];

int main()
{
    int n, i, j, nr;

    in >> n;

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


    return 0;
}