# include <iostream>

using namespace std;

const int dim = 1001;
int n, s, E[dim];

int main ()

{
        cin >> n;
        E[0] = 1;
        E[1] = 1;
        for ( int i = 2; i <= n; ++i)
            if (E[i] == 0) {
                ++s;
                for ( int j = i + i; j <= n; j += i)
                E[j] = 1;
            }
        cout << s;
return 0;
}