const
  ch: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');
  num: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,l1,l2:longint;
  s,s1,s2:string;
  a,b,c:array[0..1000]of longint;

procedure init;
var
  i,l:longint;
begin
  readln(n);
  readln(s1);
  readln(s2);
  l1:=length(s1);
  l2:=length(s2);
  if l1<l2 then
  begin
    l:=l1;
    l1:=l2;
    l2:=l;

    s:=s1;
    s1:=s2;
    s2:=s;
  end;
  for i:=1 to l1 do
  begin
    if s1[i] in ['0'..'9'] then val(s1[i],a[l1-i+1])
    else a[l1-i+1]:=num[s1[i]];
  end;

  for i:=1 to l2 do
  begin
    if s2[i] in ['0'..'9'] then val(s2[i],b[l2-i+1])
    else b[l2-i+1]:=num[s2[i]];
  end;
end;

procedure jia;
var
  i:longint;
begin
  for i:=1 to l1 do
  begin
    c[i+1]:=c[i+1]+((a[i]+b[i]+c[i]) div n);
    c[i]:=((a[i]+b[i]+c[i]) mod n);
  end;
  if c[l1+1]>0 then inc(l1);
end;

procedure print;
var
  i:longint;
begin
  for i:=l1 downto 1 do
  begin
    if c[i]<10 then write(c[i])
    else write(ch[c[i]]);
  end;
  writeln;
end;

begin
  assign(input,'madition.in'); reset(input);
  assign(output,'madition.out'); rewrite(output);
  init;
  jia;
  print;
  close(input);
  close(output);
end.