#define rep(i,n) for(int i=0;i<(int)(n);i++)
#define ALL(v) v.begin(),v.end()
typedef long long ll;
 
#include<bits/stdc++.h>
using namespace std;

int main(){
  ios::sync_with_stdio(false);
  std::cin.tie(nullptr);
 
  int n;
  string s,t;
  cin>>n>>s>>t;
  if(s[0]!=t[0] || s[n-1]!=t[n-1]){
    cout<<-1<<endl;
    return 0;
  }
  
  vector<int> A(n-1),B(n-1);
  rep(i,n-1){
    if(s[i]==s[i+1]) A[i]=0;
    else A[i]=1;
    if(t[i]==t[i+1]) B[i]=0;
    else B[i]=1;
  }
  int c1=0,c2=0;
  rep(i,n-1){
    if(i%2) A[i]^=1,B[i]^=1;
    if(A[i]) c1++;
    if(B[i]) c2++;
  }
  if(c1!=c2){
    cout<<-1<<endl;
    return 0;
  }
  ll ans=0;
  vector<int> C,D;
  rep(i,n-1){
    if(A[i]) C.push_back(i);
    if(B[i]) D.push_back(i);
  }
  int c=C.size();
  rep(i,c){
    ans+=abs(C[i]-D[i]);
  }
  cout<<ans<<endl;

  return 0;
}