import std.conv, std.functional, std.range, std.stdio, std.string;
import std.algorithm, std.array, std.bigint, std.bitmanip, std.complex, std.container, std.math, std.mathspecial, std.numeric, std.regex, std.typecons;
import core.bitop;

class EOFException : Throwable { this() { super("EOF"); } }
string[] tokens;
string readToken() { for (; tokens.empty; ) { if (stdin.eof) { throw new EOFException; } tokens = readln.split; } auto token = tokens.front; tokens.popFront; return token; }
int readInt() { return readToken.to!int; }
long readLong() { return readToken.to!long; }
real readReal() { return readToken.to!real; }

bool chmin(T)(ref T t, in T f) { if (t > f) { t = f; return true; } else { return false; } }
bool chmax(T)(ref T t, in T f) { if (t < f) { t = f; return true; } else { return false; } }

int binarySearch(alias pred, T)(in T[] as) { int lo = -1, hi = cast(int)(as.length); for (; lo + 1 < hi; ) { const mid = (lo + hi) >> 1; (unaryFun!pred(as[mid]) ? hi : lo) = mid; } return hi; }
int lowerBound(T)(in T[] as, T val) { return as.binarySearch!(a => (a >= val)); }
int upperBound(T)(in T[] as, T val) { return as.binarySearch!(a => (a > val)); }


long solve(const(int) N, const(string) S, const(string) T) {
  if (S[0] != T[0]) return -1;
  if (S[N - 1] != T[N - 1]) return -1;
  int[] xs, ys;
  foreach (i; 0 .. N - 1) {
    if (((i & 1) != 0) == (S[i] != S[i + 1])) xs ~= i;
    if (((i & 1) != 0) == (T[i] != T[i + 1])) ys ~= i;
  }
  const len = cast(int)(xs.length);
  if (len != ys.length) {
    return -1;
  }
  long ans;
  foreach (j; 0 .. len) {
    ans += abs(ys[j] - xs[j]);
  }
  return ans;
}

void main() {
  debug {{
    enum lim = 8;
    foreach (n; 1 .. lim + 1) {
      auto dist = new int[][](1 << n, 1 << n);
      foreach (u; 0 .. 1 << n) {
        dist[u][] = 1 << n;
        dist[u][u] = 0;
      }
      foreach (u; 0 .. 1 << n) {
        foreach (i; 1 .. n - 1) {
          if ((u >> (i - 1) & 1) == (u >> (i + 1) & 1)) {
            chmin(dist[u][u ^ 1 << i], 1);
          }
        }
      }
      foreach (w; 0 .. 1 << n) foreach (u; 0 .. 1 << n) foreach (v; 0 .. 1 << n) {
        chmin(dist[u][v], dist[u][w] + dist[w][v]);
      }
      foreach (u; 0 .. 1 << n) foreach (v; 0 .. 1 << n) {
        if (dist[u][v] >= 1 << n) {
          dist[u][v] = -1;
        }
      }
      foreach (u; 0 .. 1 << n) foreach (v; 0 .. 1 << n) {
        const string su = iota(n).map!(i => "01"[u >> i & 1]).array;
        const string sv = iota(n).map!(i => "01"[v >> i & 1]).array;
        const slv = solve(n, su, sv);
        assert(dist[u][v] == slv, format("%s %s: %s %s", su, sv, dist[u][v], slv));
      }
    }
  }}
  
  try {
    for (; ; ) {
      const N = readInt;
      const S = readToken;
      const T = readToken;
      
      const ans = solve(N, S, T);
      writeln(ans);
    }
  } catch (EOFException e) {
  }
}