View Code of Problem 3920

#include<iostream>
#include<cstring>
#include<algorithm>
#include<queue>
#include<stdio.h>
#include<string.h>
#include<cmath>
using namespace std;
int main()
{
  int times;
  cin>>times;
  while(times--)
  {
      long long n,m;
      cin>>n>>m;
      if(n<m)
        cout<<0<<endl;
      else {
        long long sum=0,tem=0,cnt=0;
        tem=n/(m*10);//有几个10倍
        for(int i=1;i<=10;i++)
        {
            cnt+=(m*i)%10;
        }
       // cout<<cnt<<"**"<<endl;
        sum=tem*cnt;//几个10倍里面加完了;
        tem=m;cnt=n%(m*10);
        int id=1;
        //cout<<tem<<" ---   "<<cnt<<"//"<<sum<<endl;
        while(tem<=cnt)
        {
            sum+=tem%10;
            id++;tem=m*id;

        }
        cout<<sum<<endl;
  }}

   return 0;
}