# 【題解】CSES 1195 Flight Discount

```#include <iostream>
#include <vector>
#include <queue>
using namespace std;

int n, m, a, b;
long long c, dis[2][100005];
vector <pair<long long, int> > v[100005];

int main() {
cin >> n >> m;
for (int i = 0; i < m; i++){
cin >> a >> b >> c;
v[a].push_back({c, b});
}
for (int i = 1; i <= n; i++){
dis[0][i] = 1e18;
dis[1][i] = 1e18;
}
dis[0][1] = 0;
priority_queue <pair<long long, pair<int, int> >, vector<pair<long long, pair<int, int> > >, greater<pair<long long, pair<int, int> > > > pq;
pq.push({0, {1, 0}});
while (!pq.empty()){
auto now = pq.top();
pq.pop();
if (now.first > dis[now.second.second][now.second.first]) continue;
for (auto i:v[now.second.first]){
if (dis[now.second.second][i.second] > now.first + i.first){
dis[now.second.second][i.second] = now.first + i.first;
pq.push({dis[now.second.second][i.second], {i.second, now.second.second}});
}
if (now.second.second == 0){
if (dis[1][i.second] > now.first + i.first/2){
dis[1][i.second] = now.first + i.first/2;
pq.push({dis[1][i.second], {i.second, 1}});
}
}
}
}
cout << dis[1][n] << "\n";
}
```