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

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

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

def divide(a, b):
    if b == 0:
        print 'Cannot divide by zero.'
    else:
        c = a / b
        return c

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

        if d == 'q':
            break
        if not (d == 'a' or d == 's' or d == 'm' or d == 'd' or d == 'q'):
            print 'WHAT ARE YOU DOING?'
            continue
        a = float(raw_input('First number: '))
        b = float(raw_input('Second number: '))

        if d == 'a':
            plussa = add(a, b)
            print plussa

        if d == 's':
            miinus = subtract(a, b)
            print miinus

        if d == 'm':
            kerto = multiply(a, b)
            print kerto

        if d == 'd':
            jako = divide(a, b)
            print jako

if __name__ == '__main__':
    main()