#pragma GCC optimize("Ofast")
//#pragma GCC optimize("unroll-loops")
//#pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,fma,abm,mmx,avx,avx2,tune=native")
#include<bits/stdc++.h>
using namespace std;
/*#include<ext/pb_ds/assoc_container.hpp>
#include<ext/pb_ds/tree_policy.hpp>
using namespace __gnu_pbds;
/*template <typename T>
using ordered_set = tree<T, null_type, less<T>, rb_tree_tag, tree_order_statistics_node_update>;
*/typedef long long ll;
typedef unsigned long long ull;
typedef long double ld;
typedef pair<ll,ll> pl;
typedef pair<int,int> pii;

#define int ll
#define LOCAL 0
#define dbg(x) cout << #x << " is " << x << "\n"
#define gll(x) scanf("%d",&x)
#define gll2(x,y) scanf("%d%d",&x,&y)
#define gll3(x,y,z) scanf("%d%d%d",&x,&y,&z)
#define gllarr(arr,n) f(i,n) gll(arr[i]);
#define sz(x) ((int)x.size())
#define s(x) sort(x.begin(),x.end())
#define all(v) v.begin(),v.end()
#define rs(v) { s(v) ; r(v) ; }
#define r(v) {reverse(all(v));}
#define pb push_back
#define f(i,n) for(int i=0;i<n;i++)
#define fr(i,n) for(int i=n-1;i>=0;i--)
#define rep(i,a,b) for(int i=a;i<=b;i++)
#define repr(i,a,b) for(int i=a;i>=b;i--)

const ll mod = 998244353;
const ll inf = (ll)1e16;
const ld eps = 1e-12;
const ll N = (int)1e5 + 5;
const ll LOGN = 19;
const ld PI = 3.14159265358979323846;
inline ll mul(ll a, ll b, ll m = mod) { return (ll)(a * b) % m;}
inline ll add(ll a, ll b, ll m = mod) { a += b; if(a >= m) a -= m; if(a < 0) a += m; return a;}
inline ll power(ll a, ll b, ll m = mod) { if(b == 0) return 1; if(b == 1) return (a % m); ll x = power(a, b / 2, m); x = mul(x, x, m); if(b % 2) x = mul(x, a, m); return x;}

int n, m, dist[N];
bool vis[N], done[N];
vector< pair<int, pair<int, int> > > a;
vector< pair<int, int> > start[N];
priority_queue< pair<int, int>, vector<pair<int,int> >, greater<> > Q;

void solve() {
    int last = 0;
    f(i, n + 4) dist[i] = inf, vis[i] = done[i] = false;
    dist[0] = 0;
    vis[0] = true;
    done[0] = true;
    for(auto &it: start[0]) {
        Q.push(it);
        dist[it.second] = it.first;
    }
    while(!Q.empty()) {
        auto it = Q.top();
        Q.pop();
        int u = it.second;
       // dbg(u);
        if(vis[u]) continue;
        vis[u] = true;
        if(u == n - 1) break;
        for(int tt = last + 1; tt <= u; tt++) {
            if(done[tt]) continue;
            done[tt] = true;
            for(auto &qt: start[tt]) {
                int v = qt.second;
                int w = qt.first;
                if(dist[u] + w < dist[v]) {
                    dist[v] = dist[u] + w;
                    Q.push({dist[v], v});
                }
            }
        }  
        last = u;
    }
    // f(i, n) cout<<dist[i]<<' ';
    // cout<<endl;
    if(dist[n - 1] == inf) cout<<"-1";
    else cout<<dist[n - 1];
}

int32_t main() {
    ios_base::sync_with_stdio(false);
    cin.tie(NULL);
    if (LOCAL) {
        freopen("C:\\Users\\Dishant\\Desktop\\Collection-DEV c++\\input.txt", "r", stdin);
        freopen("C:\\Users\\Dishant\\Desktop\\Collection-DEV c++\\output.txt", "w", stdout);
    }
    cin>>n>>m;
    f(i, m) {
        int u, v, w;
        cin>>u>>v>>w;
        u--, v--;
        a.pb({u, {v, w}});
        start[u].pb({w, v});
    }
    solve();
    return 0;
}

Measured memory_bytes: 11824