#include<bits/stdc++.h>
using namespace std;
#define ll long long
#define FOR(i, a, b) for (int i = (a), _b = (b); i <= _b; i++)
#define FORD(i, b, a) for (int i = (b), _a = (a); i >= _a; i--)
#define pa pair<ll, ll>
#define fi first
#define se second
#define bit(mask, j) ((mask >> j) & 1)
const ll mod = 1e9 + 7;
const ll INF = 1e18;
//--------------------------------------------------------------------
const ll N = 3e5 + 10;
struct ED {
ll u, v, w;
} ed[N];
vector<pa> g[N];
ll n, m;
namespace sub3 {
bool check() {
return m == n - 1;
}
ll f[N];
bool dx[N];
pa par[N];
void dfs(ll u, ll p) {
for(auto e : g[u]) {
ll v = e.fi, id = e.se;
if(v == p) continue;
par[v] = {u, id};
f[v] = f[u] + ed[id].w;
dfs(v, u);
}
}
void slove() {
FOR(i, 1, m) {
ll u = ed[i].u, v = ed[i].v, w = ed[i].w;
g[u].push_back({v, i});
g[v].push_back({u, i});
}
dfs(1, 0);
vector<ll> vt;
ll u = n;
while(u != 1) {
ll v = par[u].fi, id = par[u].se;
dx[id] = 1;
u = v;
}
ll ans = f[n];
ll mx = -INF;
FORD(i, m, 1) {
if(dx[i]) {
ans = max(ans, f[n] + mx);
}
mx = max(ed[i].w, mx);
}
cout << ans;
}
}
namespace sub1 {
bool check() {
return n <= 2000 && m <= 2000;
}
const ll N = 2003;
ll d[N];
void DJK() {
priority_queue<pa, vector<pa>, greater<pa>> q;
q.push({0, 1});
fill(d + 1, d + n + 1, INF);
d[1] = 0;
while(!q.empty()) {
ll u = q.top().se, du = q.top().fi;
q.pop();
if(du != d[u]) continue;
for(auto e : g[u]) {
ll v = e.fi, w = ed[e.se].w;
if(d[v] > d[u] + w) {
d[v] = d[u] + w;
q.push({d[v], v});
}
}
}
}
void slove() {
FOR(i, 1, m) {
ll u = ed[i].u, v = ed[i].v, w = ed[i].w;
g[u].push_back({v, i});
g[v].push_back({u, i});
}
DJK();
ll ans = d[n];
ll mx = ed[m].w;
FORD(i, m - 1, 1) {
ed[i].w = ed[i].w + mx;
DJK();
ans = max(ans, d[n]);
ed[i].w = ed[i].w - mx;
mx = max(ed[i].w, mx);
}
cout << ans;
}
}
namespace subend {
ll c[N];
ll d[N][2];
void DJK() {
priority_queue<pair<ll, pa>, vector<pair<ll, pa>>, greater<pair<ll, pa>>> q;
q.push({0, {1, 0}});
memset(d, 0x3f, sizeof d);
d[1][0] = 0;
while(!q.empty()) {
ll du = q.top().fi, u = q.top().se.fi, t = q.top().se.se;
q.pop();
if(du != d[u][t]) continue;
for(auto e : g[u]) {
ll v = e.fi, id = e.se;
if(t == 0) {
ll val1 = ed[id].w;
ll val2 = c[id];
if(d[v][0] > d[u][0] + val1) {
d[v][0] = d[u][0] + val1;
q.push({d[v][0], {v, 0}});
}
else {
if(d[v][1] > d[u][0] + val1 + val2) {
d[v][1] = d[u][0] + val1 + val2;
q.push({d[v][1], {v, 1}});
}
}
}
else {
ll val1 = ed[id].w;
if(d[v][1] > d[u][1] + val1) {
d[v][1] = d[u][1] + val1;
q.push({d[v][1], {v, 1}});
}
}
}
}
}
void slove() {
FOR(i, 1, m) {
ll u = ed[i].u, v = ed[i].v, w = ed[i].w;
g[u].push_back({v, i});
g[v].push_back({u, i});
}
ll mx = ed[m].w;
c[m] = INF;
FORD(i, m - 1, 1) {
c[i] = mx;
mx = max(mx, ed[i].w);
}
DJK();
cout << d[n][1] << '\n';
}
}
void hbmt() {
cin >> n >> m;
FOR(i, 1, m) {
ll u, v, w;
cin >> u >> v >> w;
ed[i] = {u, v, w};
}
// if(sub1::check()) return sub1::slove();
// if(sub3::check()) return sub3::slove();
return subend::slove();
}
int main() {
ios_base::sync_with_stdio(0);
cin.tie(0);cout.tie(0);
#define NAME "hbmt"
if(fopen(NAME".inp", "r")) {
freopen(NAME".inp", "r", stdin);
freopen(NAME".out", "w", stdout);
}
//int t;cin>>t;while(t--)
hbmt();
return 0;
}
