class Solution 
{
public:
    int maxProfit(vector<int> &prices) 
    {
        if(prices.empty())
            return 0;

        int max = 0;
        int start = prices[0];
        int last = prices[0];
        int sz = prices.size();
        for(vector<int>::size_type st = 1; st < sz; st ++)
        {
            if(prices[st] >= last)
            {
                last = prices[st];
                if(st == sz-1)// end
                    max += (last-start);
            }
            else
            {
                max += (last-start);
                start = prices[st];
                last = prices[st];
            }
        }
        return max;
    }
};