Poj Solution 3406

http://poj.org/problem?id=3406

//* @author: 82638882@163.com
import java.util.Scanner;
public class Main
{
 public static void main(String[] args)
 {
   Scanner in=new Scanner(System.in);
   int[] b2=new int[]{6,2,4,8};
   int[] b3=new int[]{1,3,9,7};
   int[] b7=new int[]{1,7,9,3};
   int[] b9=new int[]{1,9,1,9};
   int n=in.nextInt();
   int m=in.nextInt();
   int w=n-m;
   int e,a2=0,a3=0,a5=0,a7=0,a9=0;
   e=n;while((e=e/2)!=0) a2+=e;
   e=m;while((e=e/2)!=0) a2-=e;
   e=w;while((e=e/2)!=0) a2-=e;
   e=n;while((e=e/5)!=0) a5+=e;
   e=m;while((e=e/5)!=0) a5-=e;
   e=w;while((e=e/5)!=0) a5-=e;
   a3=f(n,3)-f(m,3)-f(w,3);
   a7=f(n,7)-f(m,7)-f(w,7);
   a9=f(n,9)-f(m,9)-f(w,9);
   int ans=1;
   if(a5>a2) System.out.println(5);
   else{
    a2-=a5;
    if(a2!=0){
         a2=a2%4;
      ans*=b2[a2];
      ans=ans%10;
    }
    ans*=b3[(a3%4+4)%4];
    ans=ans%10;
    ans*=b7[(a7%4+4)%4];
    ans=ans%10;
    ans*=b9[(a9%4+4)%4];
    ans=ans%10;
    System.out.println(ans);
    }
  }

  public static int f(int n,int a)
  {
    if(n==0) return 0;
    else return f(n/2,a)+g(n,a);
   }

  public static int g(int n,int a)
  {
    if(n==0)return 0;
    else if(n%10< a)return n/10+g(n/5,a);
    else return n/10+1+g(n/5,a);
  }
}