public static int twoStacks(int maxSum, List<Integer> a, List<Integer> b) {
    // Write your code here
    Stack<Integer> st1 = new Stack<>();
    Stack<Integer> st2 = new Stack<>();
    for(int i=0; i<a.size(); i++){
      st1.push(a.get(i));
    }
    for(int i=0; i<b.size(); i++){
      st2.push(b.get(i));
    }
    int lengthB=0;
    int sum = 0;
    while(lengthB<b.size() && (sum+b.get(lengthB)) <= maxSum ){
      sum += b.get(lengthB);
      lengthB++;
    }
    int maxScore = lengthB;
    for(int i=0; i<a.size(); i++){
      sum += a.get(i);
      while( sum > maxSum && lengthB > 0){
        lengthB--;
        sum -= b.get(lengthB);
      }
      if(sum>maxSum){
        break;
      }
      maxScore = Math.max( maxScore,lengthB + i+1 );
    }
    return maxScore;

    }