You make a trigger that does exactly that.
Event - Player 1 types as an exact match -
Conditions - Substring of typed string equal to "-" at (0,1)
Actions - Set HeroKillsNeeded to substring of type string at (1,3)
HeroKillsNeeded is a integer variable.
Then, you make another trigger counting the number of kills each player gets. When that number >= HeroKillsNeeded, you run victory for the player with the kills and defeat for everyone else.