public static long stockmax(List<int> prices)
{
    var profit = 0L;
    var max = prices.Count()-1;
    while(max > 0){
        var i = max-1;
        while(i >= 0 && prices[i] <= prices[max]){
            profit += prices[max] - prices[i];
            i--;
        }
        max = i;
    }
    return profit;
}