there is my code:
program z1501;
Var s,s1,s2:string;
    i,l,n:longint;
    p:shortint;
    st:boolean;
begin
 readln(n);
 readln(s);
 readln(s1);
 s:=s+'   ';
 s1:=s1+'   ';
 s2:=''; i:=1; l:=1;
st:=false;
 while True do begin
 while ((i<=n)or(l<=n))and not st do begin
       if (p=-1)and(s[i]='1')and(s[i+1]='1')and(s[i+2]='0')then begin
          s2:=s2+'11'; inc(i,2); p:=1;
          break;
       end;
       if (p=-1)and(s1[l]='1')and(s1[l+1]='1')and(s1[l+2]='0')then begin
          s2:=s2+'22'; inc(l,2); p:=1;
          break;
       end;
       if (p=1)and(s[i]='0')and(s[i+1]='0')and(s[i+2]='1')then begin
          s2:=s2+'11'; inc(i,2); p:=-1;
          break;
       end;
       if (p=1)and(s1[l]='0')and(s1[l+1]='0')and(s1[l+2]='1')then begin
          s2:=s2+'22'; inc(l,2); p:=-1;
          break;
       end;

       if (p=-1)and(s[i]='1')and(s[i+1]='0')then begin
          s2:=s2+'1'; inc(i); p:=0;
          break;
       end;
       if (p=-1)and(s1[l]='1')and(s1[l+1]='0')then begin
          s2:=s2+'2'; inc(l); p:=0;
          break;
       end;
       if (p=1)and(s[i]='0')and(s[i+1]='1')then begin
          s2:=s2+'1'; inc(i); p:=0;
          break;
       end;
       if (p=1)and(s1[l]='0')and(s1[l+1]='1')then begin
          s2:=s2+'2'; inc(l); p:=0;
          break;
       end;

       if (p=0)and(s[i]='1')and(s[i+1]='0')then begin
          s2:=s2+'1'; inc(i); p:=1;
          break;
       end;
       if (p=0)and(s1[l]='1')and(s1[l+1]='0')then begin
          s2:=s2+'2'; inc(l); p:=1;
          break;
       end;
       if (p=0)and(s[i]='0')and(s[i+1]='1')then begin
          s2:=s2+'1'; inc(i); p:=-1;
          break;
       end;
       if (p=0)and(s1[l]='0')and(s1[l+1]='1')then begin
          s2:=s2+'2'; inc(l); p:=-1;
          break;
       end;

       if (p=-1)and(s[i]='1')then begin
          s2:=s2+'1'; inc(i); p:=0;
          break;
       end;
       if (p=-1)and(s1[l]='1')then begin
          s2:=s2+'2'; inc(l); p:=0;
          break;
       end;
       if (p=1)and(s[i]='0')then begin
          s2:=s2+'1'; inc(i); p:=0;
          break;
       end;
       if (p=1)and(s1[l]='0')then begin
          s2:=s2+'2'; inc(l); p:=0;
          break;
       end;

       if (p=0)and(s[i]='1')then begin
          s2:=s2+'1'; inc(i); p:=1;
          break;
       end;
       if (p=0)and(s1[l]='1')then begin
          s2:=s2+'2'; inc(l); p:=1;
          break;
       end;
       if (p=0)and(s[i]='0')then begin
          s2:=s2+'1'; inc(i); p:=-1;
          break;
       end;
       if (p=0)and(s1[l]='0')then begin
          s2:=s2+'2'; inc(l); p:=-1;
          break;
       end;
       st:=true;
 end;
 if (length(s2)=2*n)or st then
    break;
 end;
 if length(s2)=2*n then
    writeln(s2)
 else
    writeln('Impossible');
end.