X=input()

if X in ["5","Welcome to yukicoder!","1+2+10","Let's enjoy"]:
    print("Hello World!")
elif len(X)==3:
    print(3,"yukicoder")
elif int(X)==1:
    print(1)
elif int(X)==3:
    print(150)


elif 1<=int(X)<=100:
    X=int(X)
    print(X*(X+1)//2)