Multiples of 3 and 5 : Euler Project

Multiples of 3 and 5

Problem 1

If we list all the natural numbers below 10 that are multiples of 3 or 5, we get 3, 5, 6 and 9. The sum of these multiples is 23.
Find the sum of all the multiples of 3 or 5 below 1000.

Project Euler.net

Python Code

def sumMultiples():
    sumTotal = 0
    lwrBnd = 1
    uprBnd = input("Enter the upper bound:")
    uprBnd = uprBnd-1
    print ("Enter the numbers sum of whose multiples are to be found:")
    a = input("First Number:")
    b = input("Second Number:")
    lcm = 2
    while lcm > 1:
        if lcm%a == 0 and lcm%b == 0:
            break
        else:
            lcm = lcm+1
    lastTerm = a*(uprBnd/a)   
    n = lastTerm/a
    sumTotal = sumTotal + a*(n*(n+1))/2
    lastTerm = b*(uprBnd/b)
    n = lastTerm/b
    sumTotal = sumTotal + b*(n*(n+1))/2
    lastTerm = lcm*(uprBnd/lcm)
    n = lastTerm/lcm
    sumTotal = sumTotal - lcm*(n*(n+1))/2
    print "Required Sum is",sumTotal
sumMultiples()