line = gets.split(' ')
line = line.map { |x| x.to_i }

N = line[0]
X = line[1]
T = line[2]

A = N.to_f / X.to_f

if A == N / X
  total_time = (N / X) * T
else
  total_time = (N / X + 1) * T
end

p total_time