Var
    x, y, z, d: real;

function min(a, b: real): real;
begin
    if a < b then
        min := a
    else min := b;
end;

function max(a, b: real): real;
begin
    if a > b then
        max := a
    else max := b;
end;

begin
    readln(x, y, z, d);
    writeln(max(min(x, y), max(min(x, z), min(z, d))));
end.