uses crt;
var f:text; i,j,n,m,kq,t:longint; a:array[1..100000]of longint;
begin
clrscr;
   assign(f,'BUYGIFTS.INP');reset(f);
      readln(f,n,m);
      for i:=1 to n do read(f,a[i]);
   close(f);
   assign(f,'BUYGIFTS.OUT');rewrite(f);
      for i:=1 to n-1 do
         for j:=i+1 to n do 
            if a[i]>a[j] then 
               begin t:=a[i]; a[i]:=a[j]; a[j]:=t; end;
      kq:=high(longint);
      for i:=1 to n-m+1 do 
         if a[i+m-1]-a[i]<kq then kq:=a[i+m-1]-a[i];
      write(f,kq);
   close(f); 
end.

uses math;
var a:array[0..10000007] of int64;
    n,m,mi:int64;
    i:longint;
procedure sort(l,r:int64);
var i,j,x,tmp:int64;
begin
i := l; j := r; x := a[(i+j) div 2];
 repeat
   while a[i] < x do inc(i);
   while a[j] > x do dec(j);
   if (i <= j) then
     begin
        tmp := a[i];
        a[i] := a[j];
        a[j] := tmp;
        inc(i);dec(j);
     end;
 until (i > j);
if (l<j) then sort(l,j);
if (i<r) then sort(i,r);
end;
begin
assign(input,'buygifts.inp');reset(input);
assign(output,'buygifts.out');rewrite(output);
 readln(m,n);
mi := trunc(1e18);
for i := 1 to n do read(a[i]);
sort(1,n);
for i := 1 to n-m+1 do
mi := min(mi,a[i+m-1]-a[i]);
writeln(mi);
close(input);close(output);
end.