与R中的下一行比较后，更改一行中的值

I have a dataframe as follows

我有一个数据帧如下

Position  Chr     Score
10101   chr1        0   
4509    chr1        3.58051     
10745   chr1        0
2344    chr1        0
7165    chr1        -2.59335    
6752    chr1        -2.655688   
7441    chr1        0   
7588    chr1        -4.022041   
10671   chr1        0   
Pos