#include<bits/stdc++.h>
using namespace std;
const int N = 1e6 + 10;
int n, m;
int h[N], e[N], w[N], ne[N], idx;
int dist[N];
bool st[N];//
typedef pair<int, int> PII;
void add(int a, int b, int c){
e[idx] = b, w[idx] = c, ne[idx] = h[a], h[a] = idx++;
}
int dijkstra(){
memset(dist, 0x3f, sizeof dist);
priority_queue<PII,vector<PII>, greater<PII>>heap;
dist[1] = 0;
heap.push({0,1});
while(heap.size()){
auto t = heap.top();
heap.pop();
int ver = t.second, distance = t.first;
if(st[ver])continue;
st[ver] = 1;
for(int i = h[ver]; i != -1; i = ne[i]){
int j = e[i];
if(dist[j] > distance + w[i]){
dist[j] = distance + w[i];
heap.push({dist[j], j});
}
}
}
if(dist[n] == 0x3f3f3f3f)return -1;
return dist[n];
}
int main(){
scanf("%d%d", &n, &m);
memset(h, -1, sizeof h);
for(int i = 0; i < m; i++){
int a, b, c;
scanf("%d%d%d", &a, &b, &c);
add(a, b, c);
}
int t = dijkstra();
if(t == 0x3f3f3f3f)printf("-1");
else printf("%d", t);
}