#include <iostream>
#include <cmath>

# using namespace std;
# int main() {
#     long long A,B,K,C, out;
#     cin >> A >> B >> K >> C;
#     string line;
#     getline(cin, line);
#     out = (long long) pow(2, K-1)*K;
#
#     if(A!=C && B!=C ){
#         out = 0;
#     }else if(A==B) {
#         out = (K) % (long long) 1000000007;
#     }else {
#         out = (out) % (long long) 1000000007;
#     }
#     cout << out << endl;

line = input()
a, b, k, c = line.split()
a = int(a)
b = int(b)
k = int(k)
c = int(c)
out = 0
if a != c and b != c:
    out = 0
elif a == b:
    out = k
else:
    out = ((2**(k-1)) * k) % 1000000007
print(int(out))