/////////////////////////////////No.236 鴛鴦茶
    //入力文字読み取り
    var inputall = require('fs').readFileSync('/dev/stdin', 'utf8');

    //すべて受け取り改行で区切って格納
    var input = inputall.split(" ").map(Number);

    //コーヒーの比率
    var coffee_ratio = input[0];

    //紅茶の比率
    var tea_ratio = input[1];

    //コーヒーの比率
    var coffee_capacity = input[2];

    //紅茶の比率
    var tea_capacity = input[3];

    //たすき掛けで比率の計算
    var a = coffee_ratio * tea_capacity;
    var b = tea_ratio * coffee_capacity;

    //鴛鴦茶の量
    var enoutea = "";

    //条件分け
    if (a > b) {
        enoutea = coffee_capacity + (b / coffee_ratio);
    } else if (a < b) {
         enoutea = tea_capacity + (a / tea_ratio);
    } else {
        enoutea = coffee_capacity+tea_capacity
    }

    console.log(enoutea);