No more. No less.

Are you meaning as in a show that was on precisely how long we would have wanted it, and as such, did not overstay its welcome?

If that's what you mean, then I think Barney Miller would fit that criteria; that 1975-82 ABC police comedy w/Hal Linden went out on top exactly when it was supposed to in 1982, and its finale, IMO, has been one of the best I've ever seen.

The Carol Burnett Show. Harvey left, it didn't work with Dick Van Dyke, she was having problems with her daughter, it was time to leave.

Maybe The Dick Van Dyke Show. It was decided that it would last five seasons and they did five seasons. Probably would not have translated well from the Kennedy 1960’s to the Groovy 1960’s.