#include <bits/stdc++.h>
#define err(args...) {}
#ifdef DEBUG
#include "_debug.cpp"
#endif
using namespace std;
using ll = long long;
using ld = long double;
template <typename T> using lim = numeric_limits<T>;
template <typename T> istream& operator>>(istream& is, vector<T>& a) { for(T& x : a) { is >> x; } return is; }
template <typename X, typename Y> istream& operator>>(istream& is, pair<X, Y>& p) { return is >> p.first >> p.second; }
struct edge {
int u, v;
edge reverse() const { return {v, u}; }
friend ostream& operator<<(ostream& os, const edge& e) {
return os << "{u: " << e.u << ", v: " << e.v << "}";
}
};
template <bool Directed, typename TEdge, bool Index> struct graph {
using EType = TEdge;
vector<TEdge> edges;
vector<vector<int>> adj;
graph(int n) : adj(n + Index) {}
graph(int n, int m) : graph(n) { edges.reserve(m << not Directed); }
TEdge& operator()(int e) { return edges[e]; }
vector<int>& operator[](int u) { return adj[u]; }
int size() { return adj.size() - Index; }
void append(int u, const TEdge& e) {
adj[u].push_back(edges.size());
edges.push_back(e);
}
void add_edge(const TEdge& e) {
append(e.u, e);
if(not Directed) append(e.v, e.reverse());
}
};
template <typename TEdge, bool Index> pair<vector<int>, vector<vector<int>>> find_2eccs(graph<0, TEdge, Index>& g) {
vector<int> vis(g.adj.size()), low(g.adj.size()), cut_edge(g.edges.size()), s;
vector<vector<int>> _2eccs = {};
int timer = 1;
function<void(int, int)> dfs = [&](int u, int from) {
vis[u] = low[u] = timer++;
s.push_back(u);
for(int e : g[u]) {
if(not vis[g(e).v]) {
dfs(g(e).v, e & ~1);
if(vis[u] < low[g(e).v]) {
cut_edge[e] = cut_edge[e ^ 1] = true;
_2eccs.push_back(vector<int>());
do {
_2eccs.back().push_back(s.back()), s.pop_back();
} while(_2eccs.back().back() != g(e).v);
}
low[u] = min(low[u], low[g(e).v]);
} else if((e & ~1) != from and vis[u] > vis[g(e).v]) {
low[u] = min(low[u], vis[g(e).v]);
}
}
};
for(int u = Index; u < g.adj.size(); u++) if(not vis[u]) {
dfs(u, -1);
_2eccs.push_back(vector<int>());
while(not s.empty()) {
_2eccs.back().push_back(s.back()), s.pop_back();
}
}
return {move(cut_edge), move(_2eccs)};
}
template <bool Directed, typename TEdge, bool Index>
pair<vector<int>, vector<int>> bfs(graph<Directed, TEdge, Index>& g, const vector<int>& s) {
vector<int> d(g.adj.size(), lim<int>::max()), p(g.adj.size(), -1);
queue<int> q;
for(int u : s) {
d[u] = 0;
q.push(u);
}
while(not q.empty()) {
int u = q.front(); q.pop();
for(int e : g[u]) {
if(d[g(e).v] > d[u] + 1) {
d[g(e).v] = d[u] + 1, p[g(e).v] = e;
q.push(g(e).v);
}
}
}
return {move(d), move(p)};
}
int main() {
ios_base::sync_with_stdio(false);
cin.tie(0);
int n, m;
cin >> n >> m;
graph<0, edge, 1> g(n, m);
edge last_edge;
for(int i = 0; i < m; i++) {
int u, v, w;
cin >> u >> v >> w;
g.add_edge(last_edge = {min(u, v), max(u, v)});
}
graph<0, edge, 1> sp_dag(n);
auto [ds, ps] = bfs(g, {1});
auto [dt, pt] = bfs(g, {n});
for(auto [u, v] : g.edges) {
if(ds[u] + 1 + dt[v] == ds[n]) {
sp_dag.add_edge({min(u, v), max(u, v)});
}
}
auto [cut_edge, _2eccs] = find_2eccs(sp_dag);
bool increase = false;
for(int i = 0; i < sp_dag.edges.size(); i += 2) {
edge& sp_edge = sp_dag.edges[i];
increase |= cut_edge[i] and (sp_edge.u != last_edge.u or sp_edge.v != last_edge.v);
}
cout << ds[n] + increase << endl;
return 0;
}
