#include <iostream>
#include <vector>
#include <cmath>

int prime(int number) {
    int s_num = sqrt(number);
    if (number == 2) {
        return 1; 
    } else if (number % 2 == 0) {
        return 0;
    }
    for (int i = 3; i <= s_num; i += 2) {
        if (number % i == 0) {
            return 0;
        }
    }
    return 1;
}

int main(void) {
    int number;
    int count = 0;
    int max = 1;

    std::vector<int> v(1000000, 0);

    while (std::cin >> number) {
        if (number > max) {
            for (int i = max + 1; i <= number; i++) {
                if (prime(i) == 1) {
                    count++;
                }
                v[i - 1] = count;
                max = number;
            }
        }
        std::cout << v[number - 1] << std::endl;
    }
    return 0;
}