#include<bits/stdc++.h>
using namespace std;

int main(){
    int n; cin>>n;
    string s; cin >> s;
    string t; cin >> t;

    int cnt=0;
    bool flg = false;
    for(int i=0; i<s.length(); i++){
        string s_sub = s.substr(i, s.length()-i);
        for(int j=0; j<t.length(); j++){
            string t_sub = t.substr(0, t.length()-j);
                if(s_sub==t_sub){
                    cnt = s_sub.length();  flg = true;
                    break;
                }
            }
        
        if(flg) break;
    }
    string res = s + t.substr(cnt, t.length()-cnt);
    int ans = res.length();
    cout << ans << endl;
    return 0;

}
#include <algorithm>
#include <bitset>
#include <complex>
#include <deque>
#include <iostream>
#include <istream>
#include <iterator>
#include <map>
#include <queue>
#include <set>
#include <stack>
#include <string>
#include <vector>
#include <tuple>
#include <iomanip>
using namespace std;

typedef long long ll;
typedef unsigned long long ull;
typedef vector<ll> vec;
typedef vector<vec> mat;
#define rep(i, n) for(ll i = 0; i < (n); i++)
#define revrep(i, n) for(ll i = (n)-1; i >= 0; i--)
#define pb push_back
#define f first
#define s second
ll max(ll a, ll b){return (a > b) ? a : b;}
ll min(ll a, ll b){return (a < b) ? a : b;}
ll max3(ll a, ll b, ll c){return max(a, max(b, c));};
ll min3(ll a, ll b, ll c){return min(a, min(b, c));};
ll max4(ll a, ll b, ll c, ll d){return max(max(a, b), min(c, d));};
ll min4(ll a, ll b, ll c, ll d){return min(min(a, b), min(c, d));};
ll max5(ll a, ll b, ll c, ll d, ll e){return max(max(a, b), max3(c, d, e));};
ll min5(ll a, ll b, ll c, ll d, ll e){return min(min(a, b), min3(c, d, e));};

const ll INFL = 1LL << 60;//10^18 = 2^60
const int INF = 1 << 30;//10^9
ll MOD = 1000000007;
//ll MOD = 998244353;

vector<ll> dy = {0, 0, 1, -1, 1, 1, -1, -1, 0};
vector<ll> dx = {1, -1, 0, 0, 1, -1, 1, -1, 0};


ll pow_long(ll x, ll k){
  ll res = 1;
  while(k > 0){
    if(k % 2) res *= x;
    x *= x;
    k /= 2;
  }
  return res;
}
ll pow_mod(ll x, ll k){
  x %= MOD; x += MOD; x %= MOD;
  ll res = 1;
  while(k > 0){
    if(k % 2){
      res *= x; res %= MOD;
    }
    x *= x; x %= MOD;
    k /= 2;
  }
  return res;
}

ll inverse(ll x){return pow_mod(x, MOD - 2);};

ll gcd(ll a, ll b){
    if(b == 0) return a;
    return gcd(b, a % b);
}

ll lcm(ll x, ll y){return x / gcd(x, y) * y;};

ll kai_mod(ll x){
  if(x == 0) return 1;
  return x * kai_mod(x-1) % MOD;
}

/*
//コンビネーション
const int MAXcomb = 200010;
ll fac[MAXcomb], finv[MAXcomb], inv[MAXcomb];
//facはn!,finvは1/n!
//invは逆元
void COMinit(){
    fac[0] = fac[1] = 1;
    finv[0] = finv[1] = 1;
    inv[1] = 1;
    for(int i = 2; i < MAXcomb; i++){
        fac[i] = fac[i-1] * i % MOD;
        inv[i] = MOD - inv[MOD%i] * (MOD/i) % MOD;
        finv[i] = finv[i-1] * inv[i] % MOD;
    }
}
ll comb(int n, int k){
    if(n < k) return 0;
    if(n < 0 || k < 0) return 0;
    return fac[n] * finv[k] % MOD * finv[n-k] % MOD;
}
*/

ll N, M;
vector<ll> A, B;
void solve(){
  ll ans = 1;
  sort(A.begin(), A.end());
  reverse(A.begin(), A.end());
  A.pb(-1);
  sort(B.begin(), B.end());
  reverse(B.begin(), B.end());
  rep(i, N-1)if(A[i] == A[i+1]) ans = 0;
  rep(i, M-1)if(B[i] == B[i+1]) ans = 0;
  B.pb(-1);
  ll a = 0, b = 0;
  for(ll i = N * M; i >= 1; i--){
    if(A[a] == i && B[b] == i){
      ans *= 1;
      a++, b++;
    }else if(A[a] == i){
      ans *= b;
      a++;
    }else if(B[b] == i){
      ans *= a;
      b++;
    }else{
      ans *= a * b - (N*M-i);
    }
    ans %= MOD;
  }
  cout << ans << endl;
}
int main(){
  cin >> N >> M;
  A.resize(N);
  B.resize(M);
  rep(i, N) cin >> A[i];

  rep(i, M) cin >> B[i];

  solve();
}
