def main():
    print('==Assignment 4==')

    flag=True
    while flag:
        a = input("pls input number:")
        try: 
            a = int(a)
            flag=False
        except :
            print("pls input a number!")
    
    counter=0
    total=1

    while counter<a:counter+=1;total*=counter

    print(f"{a}!= {total}")

    print('==End Of Assi4==')
    return 0

if __name__ == '__main__':
    main()