#include <bits/stdc++.h>
using namespace std;
long long ans;
int n, a[1000005], b[1000005], A[1000005], B[1000005];
string s, t;
int main()
{
	cin >> n;
	cin >> s >> t;
	if (s[0] != t[0] || s[n - 1] != t[n - 1])
	{
		cout << -1;
		return 0;
	}
	for (int i = 1; i < n; i++)
	{
        if (i & 1)
        {
    		a[i] = s[i - 1] != s[i];
    		b[i] = t[i - 1] != t[i];
        }
        else
        {
    		a[i] = s[i - 1] == s[i];
    		b[i] = t[i - 1] == t[i];
        }
        ans += a[i] - b[i];
	}
    if (ans)
    {
        cout << -1;
        return 0;
    }
    for (int i = 1; i <= n; i++)
    {
        if (a[i])
        {
            A[++A[0]] = i;
        }
        if (b[i])
        {
            B[++B[0]] = i;
        }
    }
    for (int i = 1; i <= n; i++)
    {
        ans += abs(A[i] - B[i]);
    }
    cout << ans;
	return 0;
}