type vector=array[0..750000] of longint;
     long_string=array[1..500000] of char;

var n:longint;
    s,t:long_string;
    i:longint;

function qqq(s,t:long_string; n:longint):longint;
  var f:vector;
      k,i:longint;
      result:longint;
  begin
    result:=-1;
    f[1]:=0;
    k:=0;
    for i:=2 to n do
      begin
        while (k>0) and (s[k+1]<>s[i]) do k:=f[k];
        if s[k+1]=s[i] then inc(k);
        f[i]:=k;
      end;
    k:=0;
    for i:=1 to 2*n do
      begin
        while (k>0) and (s[k+1]<>t[i]) do k:=f[k];
        if s[k+1]=t[i] then inc(k);
        if k=n
          then
            begin
              result:=i+n;
              break;
            end;
      end;
    qqq:=result;
  end;

begin
  readln(n);
  for i:=1 to n do read(s[i]);
  readln;
  for i:=1 to n do read(t[i]);
  for i:=1 to n do t[n+i]:=t[i];
  writeln(qqq(s,t,n) mod n);
end.

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