#include<bits/stdc++.h>
using namespace std;
using ll = long long;
#define all(x) (x).begin(), (x).end()
int main() {
cin.tie(0)->sync_with_stdio(false);
int n, m;
cin >> n >> m;
vector<int> s(n), f(m);
vector<array<int, 2>> a;
for (int &i : s) {
cin >> i;
a.push_back({i, 0});
}
for (int &i : f) {
cin >> i;
if (!binary_search(all(s), i))
a.push_back({i, 1});
}
sort(all(a));
int A = a.size();
// next sprinkler
vector<int> nxt(A, -1);
for (int i = A - 2; i >= 0; i--) {
nxt[i] = (a[i + 1][1] == 0 ? i + 1 : nxt[i + 1]);
}
string o;
int lo = 0, hi = 1e9, ans = -1;
while (lo <= hi) {
int mid = (lo + hi) / 2;
vector<int> dp(A + 1, -1);
vector<string> used(A + 1);
auto upd = [&](int i, int j, string c) {
if (dp[j] == -1) {
dp[j] = i;
used[j] = c;
}
};
dp[0] = 0;
for (int i = 0; i < A; i++) {
if (dp[i] == -1)
continue;
auto &[x, t] = a[i];
if (t == 0) {
int j = i + 1;
while (j < A && a[j][1] == 1 && a[j][0] <= x + mid)
j++;
upd(i, j, "R");
continue;
}
if (nxt[i] != -1) {
upd(i, nxt[i] + 1, "L");
int p = nxt[i];
int q = nxt[p];
if (q != -1 && a[q][0] <= x + mid) {
int r = nxt[q];
if (r != -1 && a[r][0] <= a[p][0] + mid)
upd(i, r, "LR");
else
upd(i, upper_bound(all(a), array<int, 2> ({a[p][0] + mid, 3})) - a.begin(), "LR");
}
}
}
if (dp[A] != -1) {
string dir;
for (int i = A; i > 0; i = dp[i])
dir += used[i];
reverse(all(dir));
assert(dir.size() == n);
ans = mid, o = dir, hi = mid - 1;
} else
lo = mid + 1;
}
cout << ans << '\n';
if (ans != -1)
cout << o << '\n';
return 0;
}
