#include <bits/stdc++.h>
using namespace std;
#define int long long
#define endl '\n'

struct node {
	int a, b;
} a[200005];

bool cmp(node x, node y) {
	return x.b < y.b;
}

signed main() {
	ios::sync_with_stdio(0);
	cin.tie(0);
	cout.tie(0);
	int n, s;
	cin >> n >> s;
	for (int i = 0; i < n; i++) {
		cin >> a[i].a >> a[i].b;
	}
	sort(a, a + n, cmp);
	int c = a[0].b;
	int sum = 0, nt = 0;
	for (int i = 0; i < c; i++) {
		sum += s;
		nt++;
	}
	for (int i = 0; i < n; i++) {
		a[i].b -= nt;
	}
	for (int i = 0; i < n; i++) {
		sum += a[i].a * a[i].b;
	}
	cout << sum;



	return 0;
}