how to save a value and add, like a statistics

I have playerprefs how many popcorn caught during the game, I put the value in a scene. But when I play again and die, instead of adding to the value that was already it replaces.

example:

pipocasPerdidasNP = PlayerPrefs.GetInt ("pipocasGPE"); // I want every game add value,, if I caught 9 in the game and grabbed 10 in another game, one had to show 19

start of the game:

int currentScore = efs.GetInt ("pipocasGPE");

during game:

currentScore += additionalScore;

end game:

efs.SetInt ("pipocasGPE", cureentScore);