B0071.cpp

// Problem Code: DWNLD

#include <iostream>
#include <vector>

using namespace std;

int downloadFile(int K, vector<int> T, vector<int> D) {
	int i, min, cost;
	cost = 0;
	for(min=i=0 ; i<T.size() ; i++) {
		min += T[i];
		if(min > K) {
			T[i] = min - K;
			break;
		}
	}
	for(; i<T.size() ; i++)
		cost += T[i]*D[i];
	return cost;
}

int main() {
	int TC, N, K, num;
	vector<int> T, D;
	cin >> TC;
	while(TC--) {
		cin >> N >> K;
		for(int i=0 ; i<N ; i++) {
			cin >> num;
			T.push_back(num);
			cin >> num;
			D.push_back(num);
		}
		cout << downloadFile(K, T, D) << endl;
		T.clear();
		D.clear();
	}
	return 0;
}