a,b = map(int,input().split())
n = int(input())
P = 10 ** 9 + 7
def seki(x,y):
    l = [[0] * 2 for _ in range(2)]
    for i in range(2):
        for j in range(2):
            for k in range(2):
                l[i][j] = (l[i][j] + x[i][k] * y[k][j]) % P
    return l
A = [[a,1],[b,a]]
tmp = [[1,0],[0,1]]
while n:
    if n & 1:
        tmp = seki(tmp,A)
    n >>= 1
    A = seki(A,A)
print(tmp[0][0] * 2 % P)