#define _CRT_SECURE_NO_WARNINGS
#include<iostream>
#include<stdio.h>
#include<algorithm>
#include<vector>
#include<math.h>
#include<string>
#include<sstream>
#include<set>
#include<map>
#include<stack>
#include<queue>
#include<deque>
#include<memory.h>
#include<ctime>
#include<cassert>
#include<limits.h>
#include<unordered_map>
#include<unordered_set>

#define pb push_back
#define sz(a) (int)a.size()
#define bs binary_search
#define np next_permutation
#define mp make_pair
#define all(a) a.begin(),a.end()
#define read(a) scanf("%d", &a)
#define writeln(a) printf("%d\n", a);
#define forn(i, n) for (int i = 0; i < n; ++i)
#define forv(i, v) for (int i = 0; i < sz(v); ++i)
#define forsint(it, s) for (set<int>::iterator it = s.begin(); it != s.end(); ++it)
#define _(a, b) memset(a, b, sizeof a)
#define pii pair<int, int>
#define pll pair<long long, long long>

typedef long long ll;
typedef unsigned long long ull;

using namespace std;

template<class T> inline T sqr(T x) { return x * x; }

const double pi = acos(-1.0), eps = 1e-9, e = exp(1.0);
const int INF = 1000 * 1000 * 1000 + 7, MAXN = 100005, MOD = 1000000007, MAXBIT = 30;
const ll INFL = 1e+18;

void prepare(string s) {
#ifdef _DEBUG
	freopen("input.txt", "r", stdin);
	freopen("output.txt","w",stdout);
#else
	if (sz(s) != 0) {
		freopen((s + ".in").c_str(), "r", stdin);
		freopen((s + ".out").c_str(), "w", stdout);
	}
#endif
}

int n;
string s, t;
ll pp1[3*MAXN], pp2[3*MAXN], hs1[3*MAXN], hs2[3*MAXN], ht1[3*MAXN], ht2[3*MAXN];

long long getHash1(int l, int r) {
    long long h = ht1[r];
    if (l > 0)
        h -= ht1[l - 1];
    h *= pp1[n - 1 - r];
    return h;
}

long long getHash1s(int l, int r) {
    long long h = hs1[r];
    if (l > 0)
        h -= hs1[l - 1];
    h *= pp1[n - 1 - r];
    return h;
}

long long getHash2(int l, int r) {
    long long h = ht2[r];
    if (l > 0)
        h = (h - ht2[l - 1] + INF) % INF;
    h = (h * pp2[n - 1 - r]) % INF;
    return h;
}

long long getHash2s(int l, int r) {
    long long h = hs2[r];
    if (l > 0)
        h = (h - hs2[l - 1] + INF) % INF;
    h = (h * pp2[n - 1 - r]) % INF;
    return h;
}

void solve()
{
	cin >> n >> s >> t;

	if (sz(s) != sz(t)) {
		cout << -1;
		exit(0);
	}

	pp1[0] = pp2[0] = 1;
	for (int i = 1; i <= n; i++) {
		pp1[i] = pp1[i-1] * 53;
		pp2[i] = (pp2[i-1] * 53) % INF;
	}

	hs1[0] = s[0] - 'a' + 1;
	hs2[0] = (s[0] - 'a' + 1) % INF;
	ht1[0] = t[0] - 'a' + 1;
	ht2[0] = (t[0] - 'a' + 1) % INF;

	for (int i = 1; i < n; i++) {
		hs1[i] = hs1[i - 1] + pp1[i] * (s[i] - 'a' + 1);
		hs2[i] = (hs2[i - 1] + pp2[i] * (s[i] - 'a' + 1)) % INF;

		ht1[i] = ht1[i - 1] + pp1[i] * (t[i] - 'a' + 1);
		ht2[i] = (ht2[i - 1] + pp2[i] * (t[i] - 'a' + 1)) % INF;
	}

	for (int i = sz(t)-1; i >= 0; i--) {
		ll hashRight = getHash1(i, sz(t)-1);
		ll hashRight2 = getHash2(i, sz(t)-1);

		ll hashLeft = getHash1s(sz(t) - i, sz(t)-1);
		ll hashLeft2 = getHash2s(sz(t) - i, sz(t) - 1);

		if (hashRight == getHash1s(0, n - i - 1) && hashLeft == getHash1(0, i - 1)) {
			if (hashRight2 == getHash2s(0, n - i - 1) && hashLeft2 == getHash2(0, i - 1)) {
				cout << i;
				exit(0);
			}
		}
	}

	cout << -1;

}

int main()
{
	prepare("");

	solve();

	return 0;
}