#include <cstdio>

char p[2000010];

int sieve1(int n)
{
    int i, j, nr = 0;

    for(i = 2; i <= n; ++i)
    {
        if(p[i] == 0)
        {
            nr++;

            for(j = i + i; j <= n; j += i)
            {
                p[j] = 1;
            }
        }
    }

    return nr;
}

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

    int N; scanf("%d ", &N);

    printf("%d", sieve1(N));
}