$O(N)$暴力不就完事了。。。
```cpp
#include<cstdio>
int main()
{
long long s = 1;
int n,i;
scanf("%d",&n);
for(i=2;i<=n;i++)
{
s *= i;
while(s%10 == 0)s /= 10;
s %= 100000000;
}
printf("%lld",s%10);
return 0;
}
```
by xenonex @ 2018-08-28 00:29:23
afasf
by zmjiji @ 2018-08-28 00:35:36
@[xenonex](/space/show?uid=86061) 谢谢QAQ
by Misaka19280 @ 2018-08-28 09:59:06