aryLocation = gets.split(' ').map(&:to_i);
 
x1 = aryLocation[0];
y1 = aryLocation[1];
x2 = aryLocation[2];
y2 = aryLocation[3];
 
lengthX = x2 - x1;
lengthY = y2 - y1;
 
puts Math.sqrt(lengthX * lengthX + lengthY * lengthY).to_s