#include <iostream>
#include <stdio.h>
#include <stdlib.h>

using namespace std;

int a[2000001];

int main()
{
    freopen("ciur.in", "r", stdin);
    freopen("ciur.out", "w", stdout);

    int n;
    scanf("%d", &n);
    int sum =0;
    int current;

    for (int i=2; i<= n/2; i++){
        if (a[i] == 0) {
            current = i+i;

            while (current <=n){
                a[current] = 1;
                current +=i;
            }
        }
    }

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


    printf("%d", sum);

    return 0;
}