#include <stdio.h>

#define MAX 2000001

int primes (int A)
{
   int count = 0;
   char numbers[MAX];
   
   for (int i = 1; i <= A; ++i)
        numbers[i] = 0;

    for (int i = 2; i*i <= A; ++i)
        if (numbers[i] == 0)
        {
            count++;

            for(int j = i*i; j <= A; j +=i)
                numbers[j]++;
        }
    return count; 
}

int main ()
{
	int X;

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

    scanf ("%d", &X);
    printf("%d\n", primes(X));

    return 0;
}