uva 10212

數論問題，把2*5=10 這些都去掉 之後再乘沒乘到的就好了

//============================================================================
// Name        : The Last Non-zero Digit.cpp
// Date : 2013/4/12 下午2:06:57
// Author : 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);
    }



}