Math hypnoticsm..!!

there's a group of birds flying across the forest and stayed there for almost 3 days.. and theres another group of birds flying across the forest and stayed there..which is twice than the first group of birds.... and lastly.. only one bird flying across the forest and stayed there..for almost 3 days..!! and the sum of all birds (the first group, and second group, and 1 bird) is 100 birds overall..!!

the question is.. how many birds in the first group..???