DENDUONG PASCAL

var a:array[0..1000009] of longint;
    i,n,k:longint;
    res:real;

function max(a,b:real):real;
    begin
        if a>b then exit(a) else exit(b);
    end;

procedure sort(l,r:longint);
    var i,j,m,k,t:longint;
        begin
            i:=l;
            j:=r;
            m:=random(r-l)+l+1;
            k:=a[m];
            repeat
                while k>a[i] do inc(i);
                while k<a[j] do dec(j);
                if not(i>j) then
                    begin
                        t:=a[i];
                        a[i]:=a[j];
                        a[j]:=t;
                        inc(i);
                        dec(j);
                    end;
            until i>j;
                if l<j then sort(l,j);
                if i<r then sort(i,r);
        end;

procedure xuli;
    begin

        a[n+1]:=k;
        sort(1,n);
        res:=max(res,k-a[n]);
        res:=max(res,a[1]-0);
        for i:=2 to n do
            begin
                res:=max(res,(a[i]-a[i-1])/2);
            end;
        writeln(res:0:2);
    end;

begin
assign(input,'denduong.inp');reset(input);
assign(output,'denduong.out');rewrite(output);
readln(n,k);
for i:=1 to n do read(A[i]);

xuli;
end.