#include<stdio.h>

long n,t[2000005],i,k,p;

int main()
{	freopen("ciur.in","r",stdin);
	freopen("ciur.out","w",stdout);	
	scanf("%ld",&n);
	for(i=2;i<=n;i++)
		if(t[i]==0)
		{	k++;
			p=2;
			while(p*i<=n) 
			{ t[p*i]=1;
				p++;
			}							
		}
	printf("%ld",k);
	fclose(stdin);
	fclose(stdout);
	return 0;
	
}