#include <iostream>
#include <fstream>
#include <cstdio>

using namespace std;

FILE *f = fopen ("ciur.in", "r");
FILE *g = fopen ("ciur.out", "w");

int main()
{
    int N, i, j, nr_prime = 0;
    bool marked[1000000];
    fscanf (f, "%d", &N);
    for (i = 2; i <= N; ++i){
            if (marked[i] == 0){
                marked[i] = 1;
                nr_prime ++ ;
                for (j = i*i; j <= N; j+=i){
                    marked[j] = 1;
                }
            }
    }
    fprintf (g, "%d", nr_prime);
    return 0;
}