# A*B
def mat_mul(A, B, mod):
    C = [[0]*len(B[0]) for i in range(len(A))]
    for i in range(len(A)):
        for k in range(len(B)):
            for j in range(len(B[0])):
                C[i][j] = (C[i][j] + A[i][k]*B[k][j])%mod
    return C

#A**n
def mat_pow(A, n, mod):
    B = [[0]*len(A) for i in range(len(A))]
    for i in range(len(A)):
        B[i][i] = 1
    while n > 0:
        if n & 1 == 1:
            B = mat_mul(A, B, mod)
        A = mat_mul(A, A, mod)
        n = n>>1
    return B

# https://yukicoder.me/problems/no/891
a, b, n = map(int, input().split())
X = [0, 1]
A = [[a, b], [1, 0]]
mod = 10**9+7
A = mat_pow(A, n-1, mod)
ans = 0
for i in range(2):
    ans += A[0][i]*X[1-i]
print(ans%mod)