input = file('stdin', 'r')

l = strsplit(readLines(input, n=1), " ")

l2 = strsplit(readLines(input, n=1), " ")

x1 = as.double(l[[1]][1])

x2 = as.double(l[[1]][2])

y1 = as.double(l2[[1]][1])

y2 = as.double(l2[[1]][2])

write(sprintf("%.4f",sqrt( (((x1-y1)(x1-y1))+((x2-y2)(x2-y2))) )),'')