#include <stdio.h>
#include <stdlib.h>
#include <stdbool.h>
#include <math.h>

bool array[10000000];

int ciur_eratostene(int n){
    int p  = 0;

    for(int i = 2; i <= n; i++)
        array[i] = true;

    for(int i = 2; i <= n; i++)
        if(array[i]){
            p++;
            for(int j = i + i; j <= n; j += i)
                array[j] = false;
        }

    return p;
}

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

    scanf("%d", &n);

    printf("%d", ciur_eratostene(n));
    return 0;
}