#include <cstdio>

const int MAXN = 2000000;

char prime[MAXN + 1];

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

    int n;
    scanf("%d", &n);

    for (int i = 2; i <= n; i++) prime[i] = 1;

    int count = 0;
    for (int i = 2; i <= n; i++) {
        if (!prime[i]) continue;
        count++;
        if ((long long)i * i > n) continue;
        for (int j = i * i; j <= n; j += i) prime[j] = 0;
    }

    printf("%d\n", count);
    return 0;
}