def minimum_beads(a, b, c, k):
return max(a, b, c) * (k - 1) + 1
a, b, c, k = map(int, input().split())
print(minimum_beads(a, b, c, k))
ZGVmIG1pbmltdW1fYmVhZHMoYSwgYiwgYywgayk6CiAgICByZXR1cm4gbWF4KGEsIGIsIGMpICogKGsgLSAxKSArIDEKCmEsIGIsIGMsIGsgPSBtYXAoaW50LCBpbnB1dCgpLnNwbGl0KCkpCnByaW50KG1pbmltdW1fYmVhZHMoYSwgYiwgYywgaykpCg==