#include <iostream>
#include <cstdio>
#include <bitset>
using namespace std;

#define Nmax 2000000

int n, nr;

bitset <Nmax> ciur;

void gen(){

    for(int i = 2; i <= n; i++)
        if(!ciur[i]){

            nr++;

            for(int j = i + i; j <= n; j += i)
                ciur[j] = 1;
        }
}

void citire(){

    freopen("ciur.in", "r", stdin);

    scanf("%d", &n);
}

void afis(){

    freopen("ciur.out", "w", stdout);

    printf("%d\n", nr);
}

int main(){

    citire();
    gen();
    afis();

    return 0;
}