程序代码：

#include<iostream>
#define MAX 1000001
using namespace std;
int a[MAX];
int main()
{
   int n,i,j,m=1;
   memset(a,0,sizeof(a));
   for(i=2;i<MAX;i++)
      if(a[i]==0)
      {for(j=i;j<MAX;j+=i)a[j]=m;m++;}  
   while(scanf("%d",&n)!=EOF)
   {printf("%d\n",a[n]);}  
   return 0;
}