#include <cstdio>
#include <bitset>

using namespace std;

const int nmx = 2000002;

int n,total;
bitset <nmx> viz;

int main() {
    freopen("ciur.in", "r", stdin);
    freopen("ciur.out", "w", stdout);

    scanf("%d", &n);

    if(n >= 2)
        ++ total;

    for(int i = 3; i <= n; i += 2)
        if(not viz[i]) {
            ++ total;
            for(int j = 2 * i; j <= n; j += i)
                viz[j] = true;
        }

    printf("%d\n", total);

    return 0;
}