How Many Roosters

I have a small flock. I have 25 Rhode Island Red hens and 1 rooster. How many roosters do I need to have to take care of the 25 hens. I messed up on my initial order and got the hens right but when I went to order the random picks for my roosters. I somehow went to buff orphington chickens instead of staying rir's. I found a rooster about the same age as ny hens at a flea market that is a rir rooster but the guy only had 1. I bought it and have given the buff's away to a friend that has chickens. I want to have a purebreed stock of chickens. I bought what I thought I could handle at the start and don't have room for 10 more chickens which is about the minimum you can order and have shipped. My chickens are about 2 months old now and are doing great so I'll have to pick up roosters where I can find them close to my size to go with my chickens.