iiitv/ChefLib

// Code written by Monal
#include"bits/stdc++.h"
#include<stdio.h>
using namespace std;

int main()
{
int tc;
scanf("%d",&tc);
while(tc--)
    {
        int n,k;
        scanf("%d%d",&n,&k);
        int min[n];
        int cost[n];

        for(int i=0;i<n;++i)
        {
            scanf("%d%d",&min[i],&cost[i]);
        }
        int i=0;
        while(k>=0&&i<n)
        {
            k=k-min[i];
            if(k<0)
                min[i]=(-1)*k;
            else
                min[i]=0;
            i++;
        }
        int total=0;
        for(int j=0;j<n;++j)
        {
            total+=(min[j]*cost[j]);
        }
        printf("%d\n",total );
    }
}