import std.stdio,
       std.conv,
       std.string,
       std.range,
       std.math,
       std.algorithm;

void main()
{
    auto input = readln.split.to!(real[]);
    auto A = input[0], B = input[1], X = input[2], Y = input[3];

    auto rate = min(A, B) / max(A, B);
    auto few  = min(max(X, Y) * rate, min(X, Y));
    auto many = few * max(A, B) / min(A, B);
    "%.15s".writefln(few + many);
}