#include <iostream>
#include <fstream>

using namespace std;

const int NMAX = 2e6;

char ciur[NMAX + 1];

int main() {
    ifstream fin( "ciur.in" );
    ofstream fout( "ciur.out" );
    int n, i, j, prime = 0;
    fin >> n;
    for ( i = 2; i * i <= n; i ++ ) {
        if ( ciur[i] == 0 ) {
            for ( j = i * i; j <= NMAX; j += i ) {
                ciur[j] = 1;
            }
        }
    }
    for ( i = 2; i <= n; i ++ ) {
        prime += 1 - ciur[i];
    }
    fout << prime;
    return 0;
}