#include <iostream>
#include <cstdio>

using namespace std;

const int N = 1e6 + 10;

int primes[N], cnt;
bool st[N];

void get_primes(int n)
{
    for (int i = 2; i <= n; i ++ )
    {
        if (!st[i]) primes[cnt ++ ] = i;
        for (int j = i + i; j <= n; j += i) st[j] = true;
    }
}

int main()
{
    int x;
    scanf("%d", &x);

    get_primes(x);

    printf("%d\n", cnt);

    return 0;
}