from sys import stdin

def main():
    L, R, M = map(int, input().split())

    divl, modl = divmod(L, M)
    divr, modr = divmod(R, M)
    if divl and divr:
        ans = M
    elif not divl and not divr:
        ans = R - L
    else:
        ans = (M - L + 1) + modr
    print(ans)

input = lambda: stdin.readline()
main()