def twoStacks(maxSum, a, b):
    Totalsum = 0
    countS1 = 0 
    countS2 = 0
    result = 0
    for ele in a:
        if Totalsum + ele > maxSum:
            break
        Totalsum = Totalsum + ele
        countS1 = countS1 + 1
    for ele in b:
        Totalsum = Totalsum + ele
        countS2 = countS2 + 1
        while Totalsum > maxSum and countS1 > 0:
            Totalsum = Totalsum - a[countS1-1]
            countS1 = countS1 -1
        if Totalsum <= maxSum:
            result = max((countS1 + countS2), result)
    return result