#include <bits/stdc++.h>

using namespace std;

ifstream fin("ciur.in");
ofstream fout("ciur.out");

void ciur();

int n, cont = 0;
vector<bool> eratos(2000005, 1);


int main(){

    fin >> n;

    ciur();

    fout << cont+1;

    return 0;
}

void ciur(){
    for(int i = 3; i <= n; i += 2){
        if(eratos[i] == 1){
            cont++;

            if(i <= sqrt(n)){
                for(int j = i*i; j <= n; j += i){
                    eratos[j] = 0;
                }
            }
        }
    }
}