codeforces 869BThe Eternal Immortality

http://www.elijahqi.win/archives/1229
Even if the world is full of counterfeits, I still regard it as wonderful.

Pile up herbs and incense, and arise again from the flames and ashes of its predecessor — as is known to many, the phoenix does it like this.

The phoenix has a rather long lifespan, and reincarnates itself once every a! years. Here a! denotes the factorial of integer a, that is, a! = 1 × 2 × … × a. Specifically, 0! = 1.

Koyomi doesn’t care much about this, but before he gets into another mess with oddities, he is interested in the number of times the phoenix will reincarnate in a timespan of b! years, that is, . Note that when b ≥ a this value is always integer.

As the answer can be quite large, it would be enough for Koyomi just to know the last digit of the answer in decimal representation. And you’re here to provide Koyomi with this knowledge.
Input

The first and only line of input contains two space-separated integers a and b (0 ≤ a ≤ b ≤ 1018).
Output

Output one line containing a single decimal digit — the last digit of the value that interests Koyomi.
Examples
Input

2 4

Output

2

Input

0 10

Output

0

Input

107 109

Output

2

Note

In the first example, the last digit of is 2;

In the second example, the last digit of is 0;

In the third example, the last digit of is 2

被hack好几拨xx 心痛

求阶乘除阶乘的末尾是多少

#include<cstdio>
long long a,b;
int main(){
//  freopen("cf.in","r",stdin);
    scanf("%I64d%I64d",&a,&b);long long ans; 
    if (a==0){
        if (b>=5){
            printf("0");return 0;
        }int ans=1;
        for (int i=1;i<=b;++i) ans*=i;
        printf("%d",ans%10);return 0;
    }
    if (b-a>=10) {printf("0");return 0;}
    int a1=a%10,b1=b%10;
    if (b1<a1) {printf("0");return 0;} ans=1;
    for (int i=a1+1;i<=b1;++i) ans*=i;
    printf("%d",ans%10);
    return 0;
}