#lines = <<'EOS'
#0 0 1 1
#EOS

lines = $stdin.read

array = lines.split("\n")

str = array[0]
x1  = str.split(" ")[0].to_i
y1  = str.split(" ")[1].to_i
x2  = str.split(" ")[2].to_i
y2  = str.split(" ")[3].to_i

diff = ((x1-x2)**2).abs + ((y1-y2)**2).abs
d    = Math.sqrt(diff)
puts "#{d}"