#include<fstream>
using namespace std;

ifstream cin("ciur.in");
ofstream cout("ciur.out");

int n, f[2000002], cnt;

int main(){

    cin >> n;
    for(int i = 2; i <= n; ++i)
        f[i] = 1;

    for(int i = 2; i <= n; ++i){
        if(f[i]){
            ++cnt;
            for(int j = i + i; j <= n; j += i)
                f[j] = 0;
        }
    }

    cout << cnt;

    return 0;
}