#include <cstdio>
#include <cmath>

using namespace std;

int main() {
    int N, c, i, j, lim;
    bool v[2000005];

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

    scanf("%d", &N);
    v[2] = 1;
    for (i = 3; i <= N; i += 2) {
        v[i] = 1;
    }

    c = 1; lim = sqrt(N)+1;
    for (i = 3; i <= N; i += 2) {
        if (v[i]) {
            //printf("%d\n", i);
            ++c;
            if (i < lim) {
                for (j = i*i; j <= N; j += i) {
                    v[j] = 0;
                }
            }
        }
    }

    printf("%d", c);

    return 0;
}