Пример:
12
1 3 4 6 7 8 10 12 13 14 15 20
1 3-4 6-8 10 12-15 20
uses crt;
var N, i, s : integer;
a: array[1..100]of integer;
begin
clrscr;
write('N -> ');
readln(N);
for i:=1 to N do read(a[i]);
readln;
i:=1;
while i <= N do
begin
s:=i;
while (i < N) and (a[i] + 1 = a[i+1]) do inc(i);
if s=i then write(a[s],' ') else write(a[s],'-',a[i],' ');
inc(i);
end;
readln;
end.