# Enter your code here. Read input from STDIN. Print output to STDOUT


p = 0.5
c1 = 1000000007.0

io = raw_input().strip()
abt = map(int, io.split(' '))

def ans(a, b, t):
    cells = 1
    for t_ in range(1,t+1):
        c = p*a*t_ + p*b*t_
        cells = c % c1
    print int(cells)

ans(abt[0], abt[1], abt[2])