#include <vector>
#include <stdio.h>

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

    int number;
    scanf("%d", &number);
    std::vector<int> primes;
    std::vector<int> checked;
    int result = 0;

    for(int i = 0; i <= number; i++){
        primes.push_back(0);
        checked.push_back(0);
    }

    for(int i = 2; i <= number; i++){
        if(primes[i] == 0 && checked[i] == 0){
            primes[i] = 1;
            result++;
            for(int j = i*2; j <=number; j+=i){
                primes[j] = 0;
                checked[j] = 1;
            }
        }
    }
    printf("%d",result);
    return 0;
}