import algorithm, sequtils, strutils

let
  n = readLine stdin
  xs = stdin.readLine
            .split
            .map(parseInt)
            .sorted
            .deduplicate(true)

if xs.len < 2:
  echo 0
  quit()

var
  d = xs[1].pred xs[0]

for i in 1..xs.high:
  d = d.min xs[i].pred xs[i.pred]

echo d