#include<fstream>
using namespace std;

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

int n, f[2000002], cnt;

int main(){

    cin >> n;
    f[0] = f[1] = 1;
    for(int i = 2; i * i <= n; ++i)
        if(f[i] == 0)
           for(int j = 2; i * j <= n; ++j)
               f[i * j] = 1;

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

    cout << cnt;
    return 0;
}