#include <bits/stdc++.h>
#define int long long
using namespace std;
int n, m;
string ans;
vector<int> s, f;
int update(int id, int l, int r) {
while (id < m && l <= f[id] && f[id] <= r) {
id++;
}
return id;
}
bool check(int x) {
vector<int> dp(n + 1);
vector<char> p(n + 1, 'L');
for (int i = 0; i < n; i++) {
dp[i + 1] = dp[i];
int upl = update(dp[i], s[i] - x, s[i]);
if (dp[i + 1] < upl) {
dp[i + 1] = upl;
p[i + 1] = 'L';
}
int upr = update(dp[i], s[i], s[i] + x);
if (dp[i + 1] < upr) {
dp[i + 1] = upr;
p[i + 1] = 'R';
}
if (i > 0) {
int uplr = update(dp[i - 1], s[i] - x, s[i - 1] + x);
if (dp[i + 1] < uplr) {
dp[i + 1] = uplr;
p[i + 1] = 'B';
}
}
}
int id = n;
while (id) {
if (p[id] == 'L') {
ans[id - 1] = 'L';
id--;
} else if (p[id] == 'R') {
ans[id - 1] = 'R';
id--;
} else {
ans[id - 2] = 'R';
ans[id - 1] = 'L';
id -= 2;
}
}
return dp[n] == m;
}
signed main() {
ios_base::sync_with_stdio(0); cin.tie(0);
cin >> n >> m;
s.resize(n);
f.resize(m);
for (int i = 0; i < n; i++) cin >> s[i];
for (int i = 0; i < m; i++) cin >> f[i];
for (int i = 0; i < n; i++) ans += '_';
int l = -1, r = 1e10;
while (r - l > 1) {
int md = (r + l) / 2;
if (check(md)) {
r = md;
} else {
l = md;
}
}
if (r == 1e10) {
cout << "-1\n";
} else {
check(r);
cout << r << "\n" << ans << "\n";
}
}
