# Enter your code here. Read input from STDIN. Print output to STDOUT
a,b,t = gets.chomp.split(' ')

amount_a = a.to_i * 0.5 * t.to_i
amount_b = b.to_i * 0.5 * t.to_i

final = (amount_a + amount_b) % (10**9 + 7)

puts final.floor