Wa - gergovia

Hi every body, my first post here
I'm getting a WA response from the judge system for the problem code GERGOVIA
http://www.spoj.pl/problems/GERGOVIA1
and here is my code:

#include <iostream>
#include <vector>
#include <utility>
#include <algorithm>
#include <math.h>
using namespace std;
int main() {
	while (true) {
		int n, units = 0;
		cin >> n;
		if (n == 0)
			break;
		// first: index, second: value
		vector<pair<int, int> > sellers, consumers;
		for (int i = 0; i < n; i++) {
			int person;
			cin >> person;
			// Seller
			if (person < 0) {
				sellers.push_back(make_pair(i, -person));
				bool stop = false;
				int sellInd = sellers.size() - 1;
				while (!stop && !consumers.empty()) {
					int consInd = consumers.size() - 1;
					if (sellers[sellInd].second < consumers[consInd].second) {
						units += (sellers[sellInd].second * abs(
								i - consumers[consInd].first));
						consumers[consInd].second -= sellers[sellInd].second;
						sellers.pop_back();
						stop = true;
					} else if (sellers[sellInd].second
							> consumers[consInd].second) {
						units += (consumers[consInd].second * abs(
								i - consumers[consInd].first));
						sellers[sellInd].second -= consumers[consInd].second;
						consumers.pop_back();
					} else {
						units += (consumers[consInd].second * abs(
								i - consumers[consInd].first));
						consumers.pop_back();
						sellers.pop_back();
						stop = true;
					}
				}
			}
			// Consumer
			else if (person > 0) {
				consumers.push_back(make_pair(i, person));
				bool stop = false;
				int consInd = consumers.size() - 1;
				while (!stop && !sellers.empty()) {
					int sellInd = sellers.size() - 1;
					if (sellers[sellInd].second < consumers[consInd].second) {
						units += (sellers[sellInd].second * abs(
								i - sellers[sellInd].first));
						consumers[consInd].second -= sellers[sellInd].second;
						sellers.pop_back();
					} else if (sellers[sellInd].second
							> consumers[consInd].second) {
						units += (consumers[consInd].second * abs(
								i - sellers[sellInd].first));
						sellers[sellInd].second -= consumers[consInd].second;
						consumers.pop_back();
						stop = true;
					} else {
						units += (consumers[consInd].second * abs(
								i - sellers[sellInd].first));
						consumers.pop_back();
						sellers.pop_back();
						stop = true;
					}
				}
			}
		}
		cout << units << endl;
	}
	return 0;
}

i wish if any one could provide me some test cases to know where exactly I'm wrong