#include <stdio.h>
#define NMax 2000005

int N, n, sol[1024], cnt;
char prim[NMax];

int main()
{
   int i, j;

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

	scanf("%d", &N);

	for (i=2; i<=N; ++i)
		if ( !prim[i] )
		{
			++n;
			for (j=i+i; j<=N; j+=i)
				prim[j] = 1;
		}

	printf("%d\n", n);
	return 0;
}