long largestRectangle(vector<int> h) {
    long maxArea;
    //base case
    if (h.empty()) {
        return 0;
    }
    //second stack to divide the current stack in two
    vector<int> a;
    //minimum element present in current stack
    int minimum = *min_element(h.begin(),h.end());
		//divide the stack
    while (h.back()!=minimum) {
        a.push_back(h.back());
        h.pop_back();
    }
    // find area using minimum value stack 
    long ar = minimum * (a.size() + h.size());
    //remove the minimum value
    h.pop_back();
    //compare the max area of current stack and that from the divided stack using recursion
    maxArea = max(ar,max(largestRectangle(a),largestRectangle(h)));
    return maxArea;
}