#include <bits/stdc++.h>

using namespace std;

int N, primes;

bool visited[2000005];

void sieve1()
{
    for(int i = 2; i <= N; i++)
    {
        if(visited[i] == false)
        {
            primes++;

            for(int j = i + i; j <= N; j += i)
            {
                visited[j] = true;
            }
        }
    }
}

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

    scanf("%d", &N);

    sieve1();

    printf("%d", primes);

    return 0;
}