#include <cstdio>
#include <bitset>

using namespace std;

const int nmx = 2000002;

bitset <nmx> viz;

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

    scanf("%d", &n);

    int tt = 1;

    for(int i = 3; i <= n; i += 2)
        if(not viz[i])
    {
        ++ tt;
        for(int j = i + i; j <= n; j += i)
            viz[j] = 1;
    }

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

    return 0;
}