Need way of entering only the last value (new values added to the list periodically) in a list:

Spreadsheet 1 contains 2 lists of say 50 entries like the following:
50 100
54 110
56 112
52 101
60 125

Spreadsheet 2 should enter:
Sum of last 2 horizontal values entered in spreadsheet 1 list (i.e.: 60+125=185)

Ignore any blank rows


Thank You