program madition;
const
  a:array[10..35]of char=('a','b','c','d','e','f','g','h','i','j','k','l','m','n','o','p','q','r','s','t','u','v','w','x','y',
  'z');
  b:array['a'..'z']of longint=(10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29
  ,30,31,32,33,34,35);
var
  n,i,l:longint;
  s1,s2:string;
  c:char;
  code:integer;
  sz1,sz2:array[0..300]of longint;
begin
  fillchar(sz1,sizeof(sz1),0);
  fillchar(sz2,sizeof(sz2),0);
  assign(input,'madition.in');
  assign(output,'madition.out');
  reset(input);
  rewrite(output);
  readln(n);
  readln(s1);
  readln(s2);
  for i:=1 to length(s1)div 2 do
  begin
    c:=s1[i];
    s1[i]:=s1[length(s1)-i+1];
    s1[length(s1)-i+1]:=c;
  end;
  for i:=1 to length(s2)div 2 do
  begin
    c:=s2[i];
    s2[i]:=s2[length(s2)-i+1];
    s2[length(s2)-i+1]:=c;
  end;
  sz1[0]:=length(s1);
  for i:=length(s1) downto 1 do
  begin
    if ('a'<=s1[i])and('a'<=s1[i]) then sz1[i]:=b[s1[i]] else val(s1[i],sz1[i],code);
  end;
  sz2[0]:=length(s2);
  for i:=length(s2) downto 1 do
  begin
    if ('a'<=s2[i])and('a'<=s2[i]) then sz2[i]:=b[s2[i]] else val(s2[i],sz2[i],code);
  end;
  if sz1[0]>sz2[0] then l:=sz1[0] else l:=sz2[0];
  for i:=1 to l do
  begin
    sz1[i]:=sz1[i]+sz2[i];
    if sz1[i]>=n then begin
      sz1[i+1]:=sz1[i+1]+(sz1[i] div n);
      sz1[i]:=sz1[i] mod n;
    end;
  end;
  if sz1[l+1]<>0 then l:=l+1;
  for i:=l downto 1 do
    if (0<=sz1[i])and(sz1[i]<=9) then write(sz1[i]) else write(a[sz1[i]]);
  close(input);
  close(output);
end.