~cpp
minsum s n
    | sum [1..n] < s = minsum s (n+1)
    | otherwise = (n, sum [1..n])

~cpp
naturalSum n = n * (n+1) `div` 2
minsum s n
    | naturalSum n < s = minsum s (n+1)
    | otherwise = (n, naturalSum n)

~cpp
take 1 [(n,naturalSum n)| n<-[1..], naturalSum n >= s]