import std.algorithm, std.container, std.conv, std.math, std.range, std.typecons, std.stdio, std.string;

auto rdsp(){return readln.splitter;}
void pick(R,T)(ref R r,ref T t){t=r.front.to!T;r.popFront;}
void readV(T...)(ref T t){auto r=rdsp;foreach(ref v;t)pick(r,v);}
void readC(T...)(size_t n,ref T t){foreach(ref v;t)v=new typeof(v)(n);foreach(i;0..n){auto r=rdsp;foreach(ref v;t)pick(r,v[i]);}}

void main()
{
  int n; readV(n);
  int[] a, b; readC(n, a, b);

  auto x = new long[](n);
  foreach (i; 0..n) x[i] = a[i]+b[i]*4;

  auto m = x.minElement;
  x[] -= m;

  writeln(x.any!(xi => xi%2 == 1) ? -1 : x.sum/2);
}