#include <bits/stdc++.h>
using namespace std;
#define ll long long
const ll mod = 1e9 + 9;
const ll mmod = 998244353;
#define vl vector<long long>
#define vll vector<vector<long long>>
ll pow(ll x, ll n, ll mod){
if (n == 0){
return 1;
}
ll half = pow(x, n / 2, mod);
ll half_square = (half * half) % mod;
if (n % 2 == 0) {
return half_square;
} else {
return (half_square * x) % mod;
}
}
ll inversion_x(ll x, ll m){
ll vysledek = pow(x,m-2);
return vysledek;
}
ll n, m;
vl f, s;
vector<char> ans;
ll count(ll l, ll r, ll index){
while(index < m && f[index] >= l && f[index] <= r){
index++;
}
return index;
}
bool dyn(ll x){
vl dp {0};
vector<char> p;
for (ll i = 0; i < n; i++){
ll ndp = dp[dp.size()-1];
char znak = 'L';
ll novy = count(s[dp[dp.size()-1]] - x, s[dp[dp.size()-1]], dp[dp.size()-1]);
ndp = max(novy, ndp);
novy = count(s[dp[dp.size()-1]], s[dp[dp.size()-1]] + x, dp[dp.size()-1]);
if (novy > ndp){
znak = 'R';
ndp = novy;
}
if (dp.size() > 1){
novy = count(s[dp[dp.size()-1]]-x, s[dp[dp.size()-2]] + x, dp[dp.size()-2]);
if (novy > ndp){
znak = 'B';
ndp = novy;
}
}
dp.push_back(ndp);
p.push_back(znak);
}
for (ll i = n-1; i >= 0; i--){
if (p[i] == 'B'){
ans[i] = 'L';
ans[i-1] = 'R';
i--;
}
else{
ans[i] = p[i];
}
}
return dp[n] == m;
}
int main(){
ios::sync_with_stdio(false);
cin.tie(nullptr);
cin >> n >> m;
for (ll i = 0; i < n; i++){
ans.push_back('L');
}
for (ll i = 0; i < n; i++){
ll num;
cin >> num;
s.push_back(num);
}
for (ll i = 0; i < m; i++){
ll num;
cin >> num;
f.push_back(num);
}
ll l, r;
l = -1;
r = 1e10;
ll mid = (l+r)/2;
while (r-l > 1){
bool test = dyn(mid);
if (test == false){
l = mid;
}
else{
r = mid;
}
mid = (l+r)/2;
}
if (r == 1e10){
cout << -1;
}
else{
dyn(r);
cout << r << "\n";
for (ll i = 0; i < ans.size(); i++){
cout << ans[i];
}
}
}
