#include <iostream>
#include <cstdio>

using namespace std;

#define Nmax 2000000/2+1

int N, contor;

char (*p) = new char [Nmax];

void citire(){

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

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

void gen(){

    contor = 1;

    for(int i = 1; ((i*i) << 1) + (i << 1) <= N; i += 1)
        if(p[i] == 0){
            for(int j = ( ( i * i ) << 1 ) + ( i << 1 ); (j << 1) + 1 <= N; j += (i << 1) + 1)
                p[j] = 1;
        }

    for(int i = 1; ( i << 1 ) + 1 <= N; ++i)
        if(p[i] == 0)
            contor++;
}

void afis(){

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

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

int main(){

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

    return 0;
}