#include <bits/stdc++.h>

using namespace std;

int N, primes = 1;

bool visited[1000005];

void sieve2()
{
    for(int i = 1; i << 1 < N; ++i)
    {
        if(visited[i] == false)
        {
            primes++;

            for(int j = ((i * i) << 1) + (i << 1); j << 1 < N; j += (i << 1) + 1)
            {
                visited[j] = true;
            }
        }
    }
}

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

    scanf("%d", &N);

    sieve2();

    printf("%d", primes);

    return 0;
}