#include <iostream>

#define NMAX (1U << 21)

int main()
{
    int n;
    int cnt = 0;
    char sieve[NMAX];

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

    std::cin >> n;

    for (int i = 2; i <= n; ++i)
        sieve[i] = 1;
    
    for (int i = 2; i <= n; ++i)
        if (sieve[i]) {
            for (int j = i + i; j <= n; j += i)
                sieve[j] = 0;

            ++cnt;
        }

    std::cout << cnt << '\n';

    return 0;
}