ABC-363 B - Japanese Cursed Doll
def getIntMap():
return map(int, input().split())
def getIntList():
return list(map(int, input().split()))
def main():
N, T, P = getIntMap()
L = getIntList()
L.sort()
L.reverse()
x = L[P - 1]
print(0 if x >= T else T - x)
if __name__ == "__main__":
main()