#include <bits/stdc++.h>

using namespace std;

int c[2000001];

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

    int n;
    scanf("%d", &n);
    for (int i = 2; i * i <= n; ++i)
        if (!c[i])
            for (int j = i * i; j <= n; j += i)
                c[j] = 1;
    int res = 0;
    for (int i = 2; i <= n; ++i)
        if (!c[i])
            ++res;
    printf("%d", res);
}