Task 14

n, m, k = map(int, input().split())
if n == 0 or m == 0 or k == 0 or k - 2 <= 0:
    print(0)
elif (n+m)%k == 0:
    avt = (n+m)//(k - 2)
    print(avt)
elif m // ((n+m)//(k - 2)) >=2 and m % ((n+m)//(k - 2)) == 0:
    avt = (n+m)//(k - 2)
    print(avt+1)
else:
    print(0)