#include <iostream>
#include <fstream>

int main(){

    std::ifstream input ("ciur.in");
    std::ofstream output ("ciur.out");

    int n;
    input >> n;

    bool arr[n+1] ;
    arr[0] = false;
    arr[1] = false;
    for (int m = 2; m <= n; m++){
        arr[m] = true;
    }

    for (int i = 2; i <= n; i++){
        if (arr[i] == true){
            for (int j = 2; i*j <= n; j++){
                arr[i*j] = false;
            }
        }
    }
    
    bool num;
    int s = 0;
    for (int k = 2; k <= n; k++){
        if (arr[k] == true){
            s++;
        }
    }
    output << s;
    

    return 0;
}