a problem i faced during learning functions in python

Question

`def isgreat(a,b):
    if(a>b):
        print("1st number is great")
    elif(b>a):
        print("2nd is great ") 
    else:
        print("equal")


def gmean(a,b):
    mean = (a+b)/2

    print(mean)

a=input("input 1st number")
b=input("input 2nd number")
isgreat(a,b)
gmean(a,b)`

in this program the line mean = (a+b)/2 didnt work saying it was unsupported operand type. it worked fine when i used it in a simple program

i was expecting that "/" to work as divide operator