#include <math.h>
#include <stdio.h>

int main()
{
	unsigned int v[148934],m=2,j=5,i=1,rm=1,n;
	v[0]=2;
	v[1]=3;

	freopen("ciur.in","r",stdin);
		scanf("%d",&n);
	fclose(stdin);

	while(j<=n)
	{
		while(j%v[i]!=0)
		{
			if(i>rm)
			{
				v[m]=j; 
				m++;
				rm =(int) sqrt(m);
				break;
			}
			i++;
		}
		i=1;
		j+=2;
	}
	freopen("ciur,out","w",stdout);
		printf("%d",m);
	fclose(stdout);
	return 0;
}