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__':