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

#define Nmax 2000002

FILE *f = fopen ( "ciur.in", "r" );
FILE *g = fopen ( "ciur.out", "w" );

bitset < Nmax > marked;
int prime = 1;

void Ciur ( int N ){

    for ( int i = 3; i <= N; i += 2 ){
        if ( !marked[i] ){
            prime++;
            for ( int j = i + i; j <= N; j += i )
                marked[j] = 1;
        }
    }
}

int main(){

    int N;

    fscanf ( f, "%d", &N );

    Ciur ( N );

    fprintf ( g, "%d", prime );

    return 0;
}