#include <cstdio>

using namespace std;

const int N = 2000005;

int n, sol;
bool prim[N];

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

    scanf("%d", &n);

    for (int i = 2; i <= n; ++i) {
        if (prim[i] == 0) {
            ++sol;
            for (int j = i + i; j <= n; j += i)
                prim[j] = 1;
        }
    }
    
    printf("%d", sol);
}