#include <stdio.h>

char p[2000000];

int sieve(int n)
{
    int i, j, nr = (n > 1);

    for(i = 3; i <= n; i += 2)
    {
        if(p[i] == 0)
        {
            ++nr;

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

    return nr;
}

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

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

    printf("%d ", sieve(N));

    return 0;
}