#include <stdio.h>

#define maxn 2000005

bool prim[maxn];
int n, c;

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

	scanf("%d", &n);

	prim[1]=1;

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

	printf("%d", c);

	return 0;
}