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()