//
//  ciurul_lui_eratostene.cpp
//  probleme
//
//  Created by Mihnea Buzoiu on 6/4/21.
//

#include <stdio.h>
#include <iostream>

using namespace std;

const int IMAX = 2000001;

bool v[IMAX];

int main(int argc, const char * argv[]) {
    
    freopen("ciur.in", "r", stdin);
    freopen("ciur.out", "w", stdout);
    
    int n;
    scanf("%d", &n);
    
    int prim = 1;
    for (int i=3; i<=n; i+=2){
        if (!v[i]){
            
            for(int j = 3*i; j <= n; j += 2*i)
                v[j] = true;
            
            prim++;
        }
    }
    
    printf("%d", prim);
}