BANHCHUNG

var a:array[0..1000000] of longint;
    i,j,m,n:longint;
procedure sort(l,r: longint);
    var
        i,j,x,y: longint;
    begin
        i:=l;
        j:=r;
        x:=a[(l+r) div 2];
        repeat
            while a[i]<x do
                inc(i);
            while x<a[j] do
                dec(j);
            if not(i>j) then
                begin
                    y:=a[i];
                    a[i]:=a[j];
                    a[j]:=y;
                    inc(i);
                    j:=j-1;
                end;
        until i>j;
        if l<j then
            sort(l,j);
        if i<r then
            sort(i,r);
    end;
begin
    // assign(input,'banhchung.inp');
    // reset(input);
    // assign(output,'banhchung.out');
    // rewrite(output);
    readln(n,m);
    for i:=1 to m do
        begin
        readln(a[i]);
        if a[i]=n then
            begin
                write(n);
                halt;
            end;
        end;
    sort(1,m);
    if a[1]>n then
        begin
            write(0);
            halt;
        end;
    i:=1;
    j:=m;
    while (a[i]+a[j]>n) and (i<>j-1) do
        dec(j);
    while (a[i]+a[j]>n) and (i+1<>j) do
        inc(i);
    if a[i]+a[j]>n then
        begin
            for j:=j to m do
                if a[j]>n then exit;
            if a[j]>n then dec(j);
            a[i]:=0;
        end;
    write(a[i]+a[j]);
end.