int findNear(int value, std::stack<int> stack)
{
    while(!stack.empty())
    {
        if(stack.top() > value)
            return stack.top();
        else
            stack.pop();
    }
    return -1;
}

using namespace std;
int main() {

    stack<int> source;
    stack<int> used;
    int top;

    for(int i = 0; i < 50000; i++)
    {
        source.push(rand() % 500);
    }

    stack<pair<int, int>> pairs;
    while(!source.empty())
    {
        top = source.top();
        pairs.push(make_pair(top, findNear(top, used)));
        used.push(top);
        source.pop();
    }
    return 0;
}