#include <cstdio>

#define N_MAX 2000001

bool visited[N_MAX];
int N, primes = 0;

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

    scanf("%d", &N);

    for (int it = 2; it <= N; ++it) {
        if (visited[it]) continue;
        ++primes;
        for (int jt = it; jt <= N; jt += it) {
            visited[jt] = true;
        }
    }

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

    return 0;
}