#include <iostream>
#include <fstream>
//using namespace std;
std::ifstream cin("ciur.in");
std::ofstream cout("ciur.out");
int n, cnt;
char prim[2000005];

int main(){
    int i, j;
    cin >> n;
    for(int i=2; i<=n; i++)
        prim[i] = 1;
    for(int i=2; i<=n; i++){
        if(prim[i]){
            cnt++;
            for(j = i+i; j<=n; j += i)
                prim[j] = 0;
        }
    }
    cout << cnt;
}