#include <stdio.h>
int n,i,j,cnt;
char prim[2000005];
int main()
{
	freopen("ciur.in","r",stdin);
	freopen("ciur.out","w",stdout);
	scanf("%d",&n);
	for(i = 2;i <= n;++i) prim[i] = 1;
	for(i = 2;i <= n;++i)
	{
		if(prim[i])
		{
			++cnt;
			for(j = i + i;j <= n;j+=i)
				prim[j] = 0;
		}
	}
	printf("%d\n",cnt);
	return 0;
	fclose(stdin);fclose(stdout);
}