//
// Created by christi on 10/24/2020.
//

#include <stdio.h>

int ciur[2000000], nr;

int main(){

    int n, i;
    FILE *in, *out;
    in = fopen ("ciur.in", "r");
    out = fopen ("ciur.out", "w");
    fscanf("%d", &n);
    for(i = 2; i <= n; i++){
        if(ciur[i] == 0){
            for(int j = i+i; j <= n; j += i)
                ciur[j] = 1;
            nr++;
        }
    }
    fprintf("%d", nr);
    return 0;
}