소프티어

const fs = require('fs');

let [bagInfo, ...jewelInfos] = fs.readFileSync('input.txt', 'utf8').trim().split('\n');

jewelInfos = jewelInfos.map(jewelInfo => jewelInfo.split(' ').map(Number)).sort((a, b) => b[1] - a[1]);

let weight = bagInfo.split(' ')[0]
let result = 0
let jewelIndex = 0;

while (weight > 0) {
    if (weight >= jewelInfos[jewelIndex][0]) {
        weight -= jewelInfos[jewelIndex][0]
        result += jewelInfos[jewelIndex][0] * jewelInfos[jewelIndex][1]
        jewelIndex++;
    } else {
        result += weight * jewelInfos[jewelIndex][1]
        weight = 0
    }
}

console.log(result)