def root(d):
    
    global arr,s
    arr=[]
    if d <=9:
        return d
    else:
        while d>0:
            arr.append(d%10)
            d = int(d /10)
        s = sum(arr)
        
        return root(s)


while True:
    try:
        d = int(input())
        

        print(root(d))
    except:
        break