#include <stdio.h>

char p[2000000];

unsigned sieve(unsigned n)
{
    register 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;
}

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

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

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

    return 0;
}