#include <stdio.h>

int p[(20000000 / 32) + 10];

unsigned sieve(unsigned n)
{
    register unsigned i, j, k, nr = 1 + (n > 2);

    for(i = 5; i * i <= n - 2; i += 6)
    {
        if((p[i >> 5] & (1 << (i & 31))) == 0)
        {
            for(j = i * i; j <= n; j += i << 1)
            {
                p[j >> 5] |= (1 << (j & 31));
            }
        }

        k = i + 2;

        if((p[k >> 5] & (1 << (k & 31))) == 0)
        {
            for(j = k * k; j <= n; j += k << 1)
            {
                p[j >> 5] |= (1 << (j & 31));
            }
        }
    }

    for(i = 5; i <= n - 2; i += 6)
    {
        nr += ((p[ i      >> 5] & (1 << ( i      & 31))) == 0) +
              ((p[(i + 2) >> 5] & (1 << ((i + 2) & 31))) == 0);
    }

    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;
}