#include <iostream>
#include <algorithm>
#include <string.h>

#define IOS std::ios::sync_with_stdio(0); std::cin.tie(0); std::cout.tie(0);

typedef long long ll;
typedef unsigned long long ull;
typedef double db;
typedef long double lb;

const int E = 1e5+5;

ll c[E],p[E],S,n;

int main() {
	IOS;
	
	int T = 1;
	//std::cin >> T;
	
	while (T--) {
		std::cin >> n >> S;
		ll cnt = 0,mip = 0x3f3f3f3f;
		for(int i = 1;i <= n;i++){
			std::cin >> c[i] >> p[i];
			cnt += c[i];
			mip = std::min(mip,p[i]); 
		}
		if(cnt <= S){
			ll ans = 0;
			for(int i = 1;i <= n;i++){
				ans += c[i] * p[i];	
			}
			std::cout << ans;
		} 
		else {
			ll ans = 0;
			ans += S * mip;
			for(int i = 1;i <= n;i++){
				ans += (p[i] - mip) * c[i];
			}
			std::cout << ans;
		}
	}
	return 0;
}

0 tps 求助