#include <iostream>
#include <algorithm>
#include <fstream>
#include <cmath>
#include <string>
#include <vector>


using namespace std;

int n;
int numz[2000002];
void ciur(int N){
    for (int i = 2; i<=N; i++){
        if (numz[i] == 0)
        for (int d = i+i; d<=N; d+=i){
            numz[d] = 1;
        };
    };
}

int main() {

    ifstream inFile("ciur.in");
    ofstream outFile("ciur.out");
    int numar, cnt(0);
    inFile>>numar;
    for (int q = 0; q<= n; q++){
        numz[q] = 0;
    }
    ciur(numar+1);
    for (int i = 2; i<= numar; i++){
        if (numz[i] == 0)
            cnt++;
    };
    outFile<<cnt;

}