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


using namespace std;

int n;
int numz[2000002];
int ciur(int N){
    int cnt(1);                                                                     // 1 - prim, 0- non prim
    for (int i = 2; i<=N; i++){
        numz[i] = 1;
    };
    for (int i = 2; i <=N; i++){
        if (numz[i] == 1){
            cnt++;
            for (int q = 2*i; q <= N; q+=i){
                numz[q] = 0;
            };
        };
    };
    return cnt;
}

int main() {

    ifstream inFile("ciur.in");
    ofstream outFile("ciur.out");
    int numar;
    inFile>>numar;
    outFile<<ciur(numar);

}