#include <stdio.h>

char p[(20000000 << 3) + 10];

unsigned sieve(unsigned n)
{
    register unsigned i, j, nr = 1;

    for(i = 3; i <= n; i += 2)
    {
        if((p[i >> 3] & (1 << (i & 7))) == 0)
        {
            nr++;

            for(j = i * i; j <= n; j += i)
            {
                p[j >> 3] |= (1 << (j & 7));
            }
        }
    }

    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;
}