const rl = require("readline").createInterface({ input: process.stdin });
var iter = rl[Symbol.asyncIterator]();
const readline = async () => (await iter.next()).value;
void (async function () {
const [n, finalX] = (await readline()).split(" ").map(Number);
const arr = [];
arr.unshift([0, 0]);
let ans = 0;
let [lastX, lastY] = (await readline()).split(" ").map(Number);
for (let i = 0; i < n - 1; i++) {
const [x, offsetY] = (await readline()).split(" ").map(Number);
const nowY = lastY + offsetY;
ans += (x - lastX) * Math.abs(nowY);
console.log(ans);
lastY = nowY;
lastX = x;
}
if (finalX > lastX) ans += (finalX - lastX) * Math.abs(lastY);
console.log(ans);
})();