import java.io.*; import java.util.*; import java.math.*; class Main236 { public static void out (Object out) { System.out.println(out); } public static void main (String[] args) throws IOException { BufferedReader br = new BufferedReader(new InputStreamReader(System.in)); String[] line = br.readLine().split(" "); int a = Integer.parseInt(line[0]); int b = Integer.parseInt(line[1]); int x = Integer.parseInt(line[2]); int y = Integer.parseInt(line[3]); if (a < b) { double d = (double)y / b * a; out(d <= x ? y + d : x + ((double)x / a * b)); } else if (b < a) { double d = (double)x / a * b; out(d <= y ? x + d : y + ((double)y / a * b)); } else { out(Math.min(x , y) * 2); } } }