def twoStacks(maxSum, a, b):
    # Write your code here
    i = j = s = 0
    
    while i < len(a) and s + a[i] <= maxSum: 
        s += a[i]
        i += 1
        
    n = maxn = i
    i -= 1
    
    while j < len(b):
        if s + b[j] <= maxSum:
            s += b[j]
            j += 1
            n += 1
            maxn = max(maxn, n)
        elif i >= 0:
               s -= a[i]
               i -= 1
               n -= 1
        else:
            break
    
    return maxn