Task 10

a = input().split()
x = list(range(int(a[0])*int(a[1])))
if int(a[2]) % 2 == 0:
    x.reverse()
    indx = (int(a[1]) * (int(a[2]) - 1) + int(a[1]) - int(a[3])) + 1
    print(x[-indx])
else:
    indx = (int(a[1]) * (int(a[2]) - 1) + int(a[3])) - 1
    print(x[indx])