#include <stdio.h>
#include <stdlib.h>

int main(){
	while(1){
		int n, m;
		int i;
		int dp[11] = {0};
		int rest;
		int ans = 0;
		int d, p;
		scanf("%d%d", &n, &m);
		if(n==0 && m==0)
			break;
		for(i=0; i<n; i++){
			scanf("%d%d", &d, &p);
			dp[p] += d;
		}
		rest = m;
		for(p=10; p>=0; p--){
			if(rest == 0){
				ans += dp[p] * p;
			}
			else if(rest >= dp[p]){
				rest -= dp[p];
			}
			else{
				ans += (dp[p] - rest) * p;
				rest = 0;
			}
		}
		printf("%d\n", ans);
	}
	return 0;
}