#include <bits/stdc++.h>
using namespace std;
const int maxn = 1e4 + 5;
const int SIGMA_SIZE = 26;
const int inf = 0x3f3f3f3f;
struct SAM {
  int sz, last;
  int g[maxn << 1][SIGMA_SIZE], pre[maxn << 1], step[maxn << 1];
  int pos[maxn << 1], right[maxn << 1], cnt[maxn << 1], ans[maxn << 1];
  void newNode(int s) {
    step[++sz] = s;
    pre[sz] = 0;
    memset(g[sz], 0, sizeof(g[sz]));
  }
  int idx(char ch) { return ch - 'a'; }
  void init() {
    sz = 0, last = 1;
    newNode(0);
  }
  void insert(char ch);
  void get_tuopu();
  void get_right(char* str);
  int solve(char* str) {
    memset(cnt, 0, sizeof(cnt));
    int p = 1, n = strlen(str);
    for (int i = 0; i < n; i++) {
      int v = idx(str[i]);
      if (g[p][v])
        p = g[p][v];
      else {
        while (p && g[p][v] == 0) p = pre[p];
        if (p == 0)
          p = 1;
        else
          p = g[p][v];
      }
      cnt[p]++;
    }
    for (int i = sz; i; i--) {
      int u = pos[i];
      cnt[pre[u]] += cnt[u];
    }
    int ret = inf;
    for (int i = 2; i <= sz; i++) {
      if (right[i] == 1 && cnt[i] == 1) ret = min(ret, step[pre[i]] + 1);
    }
    if (ret == inf) ret = -1;
    return ret;
  }
} SA;
char a[maxn], b[maxn];
int main() {
  scanf("%s%s", a, b);
  int n = strlen(a);
  SA.init();
  for (int i = 0; i < n; i++) SA.insert(a[i]);
  SA.get_tuopu();
  SA.get_right(a);
  printf("%d\n", SA.solve(b));
  return 0;
}
void SAM::insert(char ch) {
  newNode(step[last] + 1);
  int v = idx(ch), p = last, np = sz;
  while (p && !g[p][v]) {
    g[p][v] = np;
    p = pre[p];
  }
  if (p) {
    int q = g[p][v];
    if (step[q] == step[p] + 1)
      pre[np] = q;
    else {
      newNode(step[p] + 1);
      int nq = sz;
      for (int j = 0; j < SIGMA_SIZE; j++) g[nq][j] = g[q][j];
      pre[nq] = pre[q];
      pre[np] = pre[q] = nq;
      while (p && g[p][v] == q) {
        g[p][v] = nq;
        p = pre[p];
      }
    }
  } else
    pre[np] = 1;
  last = np;
}
void SAM::get_tuopu() {
  for (int i = 0; i <= sz; i++) cnt[i] = 0;
  for (int i = 1; i <= sz; i++) cnt[step[i]]++;
  for (int i = 1; i <= sz; i++) cnt[i] += cnt[i - 1];
  for (int i = 1; i <= sz; i++) pos[cnt[step[i]]--] = i;
}
void SAM::get_right(char* str) {
  int p = 1, n = strlen(str);
  for (int i = 0; i <= sz; i++) right[i] = 0;
  for (int i = 0; i < n; i++) {
    int v = idx(str[i]);
    p = g[p][v];
    right[p]++;
  }
  for (int i = sz; i; i--) {
    int u = pos[i];
    right[pre[u]] += right[u];
  }
}
