#include <cstdio>

using namespace std;

unsigned int N, primes = 1;

char visited[1000005];

void sieve2()
{
    unsigned int i, j;

    for(i = 1; ((i * i) << 1) + (i << 1) <= N; i += 1)
    {
        if((visited[i >> 3] & (1 << (i & 7))) == 0)
        {
            for(j = ((i * i) << 1) + (i << 1); (j << 1) + 1 <= N; j += (i << 1) + 1)
            {
                visited[j >> 3] |= (1 << (j & 7));
            }
        }
    }

    for(i = 1; 2 * i + 1 <= N; ++i)
    {
        if((visited[i >> 3] & (1 << (i & 7))) == 0)
        {
            ++primes;
        }
    }
}

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

    scanf("%d", &N);

    sieve2();

    printf("%d", primes);

    return 0;
}