def add(a, b):
    r = a + b
    return r

def subtract(a, b):
        r = a - b
        return r

def multiply(a, b):
    r = a * b
    return r

def divide(a, b):
    if b == 0:
        asd = "Cannot divide by zero."
        return asd
    else:
        r = a / b
        return r


def main():
    kiertaa = True
    while kiertaa:
        print "(a)dd, (s)ubtract, (m)ultiply, (d)ivide, (q)uit"
        valinta = raw_input('Give an operation: ')

        if valinta == "q":
            kiertaa = False
            break
        else:

            if valinta == 'a':
                n1 = float(raw_input('First number: '))
                n2 = float(raw_input('Second number: '))
                paska = add(n1,n2)
                print paska
                continue

if __name__ == "__main__":
    main()