记录编号	352087	评测结果	AAAAAAAAAA
题目名称	[NOIP 2015]跳石头	最终得分	100
用户昵称	CodeLyoko	是否通过	通过
代码语言	Pascal	运行时间	0.060 s
提交时间	2016-11-16 21:17:40	内存使用	0.35 MiB

var
  l,n,m,i,j,mid,max:longint;
  d:array[0..50010]of longint;

function check(a:longint):boolean;
var
  i,j,now:longint;
begin
  j:=m;
  now:=0;
  for i:=1 to n+1 do begin
    if d[i]-d[now]<a then begin
      if j>0 then j:=j-1
      else exit(false);
    end
    else now:=i;
  end;
  exit(true);
end;

procedure qsort(l,r:longint);
var
  i,j,m:longint;
begin
  m:=d[(l+r)div 2];
  i:=l;
  j:=r;
  repeat
    while d[i]<m do inc(i);
    while d[j]>m do dec(j);
    if i<=j then begin
      d[n+2]:=d[i];
      d[i]:=d[j];
      d[j]:=d[n+2];
      inc(i);
      dec(j);
    end;
  until i>j;
  if i<r then qsort(i,r);
  if j>l then qsort(l,j);
end;

begin
  assign(input,'2015stone.in');
  reset(input);
  assign(output,'2015stone.out');
  rewrite(output);
  readln(l,n,m);
  d[0]:=0;
  d[n+1]:=l;
  max:=0;
  for i:=1 to n do
    read(d[i]);
  qsort(1,n);
  i:=0;
  j:=l;
  repeat
    mid:=(i+j)div 2;
    if check(mid)=true then begin
      max:=mid;
      i:=mid;
    end
    else j:=mid;
  until i=j-1;
  if check(j)=true then writeln(j)
  else writeln(max);
  close(input);
  close(output);
end.