uva 10212 - Red Huang

數論問題，把 2*5=10 這些都去掉之後再乘沒乘到的就好了
//============================================================================  
// 名稱        : The Last Non-zero Digit.cpp  
// 日期 : 2013/4/12 下午2:06:57  
// 作者 : GCA  
//============================================================================  
#include <iostream>  
#include <cstdio>  
#include <cstring>  
#include <algorithm>  
#include <cmath>  
#include <climits>  
#include <vector>  
#include <set>  
#include <map>  
#include <queue>  
#include <cctype>  
#include <utility>  
using namespace std;  
#ifdef ONLINE\_JUDGE  
#define ll "%lld"  
#else  
#define ll "%I64d"  
#endif  
typedef unsigned int uint;  
typedef long long int Int;  
#define Set(a,s) memset(a,s,sizeof(a))  
#define Write(w) freopen(w,"w",stdout)  
#define Read(r) freopen(r,"r",stdin)  
#define Pln() printf("\\n")  
#define I\_de(x,n)for(int i=0;i<n;i++)printf("%d ",x\[i\]);Pln()  
#define De(x)printf(#x"%d\\n",x)  
#define For(i,x)for(int i=0;i<x;i++)  
#define CON(x,y) x##y  
#define Pmz(dp,nx,ny)for(int hty=0;hty<ny;hty++){for(int htx=0;htx<nx;htx++){\\  
    printf("%d ",dp\[htx\]\[hty\]);}Pln();}  
#define M 55  
#define PII pair<int,int\>  
#define PB push\_back  
#define oo INT\_MAX  
#define Set\_oo 0x3f  
#define Is\_debug true  
#define debug(...) if(Is\_debug)printf("DEBUG: "),printf(\_\_VA\_ARGS\_\_)  
#define FOR(it,c) for(\_\_typeof((c).begin()) it=(c).begin();it!=(c).end();it++)  
#define eps 1e-6  
bool xdy(double x,double y){return x>y+eps;}  
bool xddy(double x,double y){return x>y-eps;}  
bool xcy(double x,double y){return x<y-eps;}  
bool xcdy(double x,double y){return x<y+eps;}  
int min3(int x,int y,int z){  
    int tmp=min(x,y);  
    return min(tmp,z);  
}  
int max3(int x,int y,int z){  
    int tmp=max(x,y);  
    return max(tmp,z);  
}  
int n,m;  
int main() {  
    ios\_base::sync\_with\_stdio(0);  
    while(~scanf("%d%d",&n,&m)){  
        int num2=0,num5=0,ans=1;  
        for(int i=n;i>=n-m+1;i--){  
            int tmp=i;  
            for(;!(tmp&1);tmp>>=1,num2++);  
            for(;!(tmp%5);tmp/=5,num5++);  
            ans=(ans\*tmp)%10;  
        }  
        if(num2>num5){  
            int tmp=num2-num5;  
            for(int i=0;i<tmp;i++)ans=(ans\*2)%10;  
        }else{  
            int tmp=num5-num2;  
            for(int i=0;i<tmp;i++)ans=(ans\*5)%10;  
        }  
        printf("%d\\n",ans);  
    }  
  
  
  
}