type digit=0..9;
const max=500001;
var sz:array[1..max]of byte;
    n,s:longint;
procedure add(k:longint;m:digit);
var t:longint;
begin
     t:=(n-k+2)div 2;
     if odd(n-k)then
        sz[t]:=sz[t]+m*10
                else
        sz[t]:=sz[t]+m;
end;
procedure main;
var t:longint;
    a,b:digit;
    e:longint;
begin
     fillchar(sz,sizeof(sz),0);
     readln(n);
     for t:=1 to n do
         begin
              readln(a,b);
              add(t,a+b);
         end;
     for t:=1 to (n+1)div 2 do
         while sz[t]>=100 do
               begin
                    dec(sz[t],100);
                    inc(sz[t+1]);
               end;
     s:=(n+1)div 2+1;
     while (sz[s]=0)and(s>0) do
           dec(s);
     for t:=s downto 1 do
         begin
              a:=sz[t]div 10;
              b:=sz[t]mod 10;
              if a<>0 then
                 write(a)
                      else
                 if t<>s then
                    write(a);
              write(b);
         end;
     if s=0 then
        write(0);
end;
begin
     main;
end.