/*
بسم الله الرحمن الرحيم
Author:
                          (:Muhammad Aneeq:)
*/

#include <iostream>
#include <vector>
#include <algorithm>
#include <set>
using namespace std;
#define int long long
int const N=5e5+10;
vector<pair<int,int>>nei[N]={};
int ans[N]={};
int dif[N]={};
void dfs(int n)
{
	vector<pair<int,int>>f;
	for (auto [i,w]:nei[n])
	{
		if (ans[i]!=ans[n])
		{
			if (ans[i]==-1)
				f.push_back({w,i});
		}
	}
	sort(begin(f),end(f));
	for (auto i:f)
	{
		if (ans[i.second]==-1)
		{
			ans[i.second]=ans[n]^1;
			dfs(i.second);
		}
	}
}
set<pair<int,int>>S;
void bfs(int ty)
{
	while (S.size())
	{
		auto f=(*begin(S));
		S.erase(f);
		if (f.first!=dif[f.second])
			continue;
		for (auto [i,w]:nei[f.second])
			if (dif[i]>f.first+w)
			{
				dif[i]=f.first+w;
				S.insert({dif[i],i});
			}
	}
}
inline void solve()
{
	int n,m;
	cin>>n>>m;
	while (m--)
	{
		int u,v,w;
		cin>>u>>v>>w;
		nei[u].push_back({v,w});
		nei[v].push_back({u,w});
	}
	for (int i=1;i<=n;i++)
		ans[i]=-1;
	ans[1]=1;
	dfs(1);
	long long w=0;
	for (int i=0;i<2;i++)
	{
		for (int k=1;k<=n;k++)
			dif[k]=1e15+10;
		vector<int>z;
		for (int j=1;j<=n;j++)
		{
			if (ans[j]==i)
				z.push_back(j);
		}
		S={};
		for (auto j:z)
			dif[j]=0,S.insert({0,j});
		bfs(i);
		for (int i=1;i<=n;i++)
			w=max(w,dif[i]);
	}
	cout<<w<<endl;
	for (int i=1;i<=n;i++)
		cout<<(ans[i]==1?'B':'D');
	cout<<endl;
}
signed main()
{
    ios_base::sync_with_stdio(false);cin.tie(NULL);cout.tie(NULL);
        solve();
}