如何查找子字符串的位置

[cwchyt]

字符串
dfaaa我cdsfdccBd我ddfddddBeee我sdfdsfeeee我eeBf我dsf

如何查找倒数第2个“我”的位置

[dirt]

       private int GetLast2Index(string input, string sub)
        {
            string Temp = input;
            int LastIndex = input.LastIndexOf(sub);
            Temp = Temp.Substring(0, LastIndex);
            LastIndex = Temp.LastIndexOf(sub);
            return LastIndex;
        }

[DemonXHunter]

int p=s.LastIndexOf('我');
p = s.LastIndexOf('我', p);