Go: package main

import (
	"container/heap"
	"fmt"
	"runtime"
)

type Node struct {
	NowPosition          int
	DiscountTicketTCount int
	Amount               int
}

type PriorityQueueNode []*Node

func (pq PriorityQueueNode) Len() int {
	return len(pq)
}

func (pq PriorityQueueNode) Less(i, j int) bool {
	return pq[i].Amount < pq[j].Amount
}

func (pq PriorityQueueNode) Swap(i, j int) {
	pq[i], pq[j] = pq[j], pq[i]
}

func (pq *PriorityQueueNode) Push(node interface{}) {
	*pq = append(*pq, node.(*Node))
}

func (pq *PriorityQueueNode) Pop() interface{} {
	old := *pq
	n := len(old)
	item := old[n-1]
	*pq = old[0 : n-1]
	return item
}

type Point struct {
	NextPoint int
	Fee       int
}

type Memo struct {
	NowPoint             int
	DiscountTicketTCount int
}

func main() {
	var c, n, m, s, d int
	var a, b, f int

	for {
		fmt.Scan(&c, &n, &m, &s, &d)
		if c == 0 && n == 0 && m == 0 && s == 0 && d == 0 {
			break
		}
		s--
		d--
		pointMap := make([][]Point, n)
		for i := 0; i < n; i++ {
			pointMap[i] = make([]Point, 0, n)
		}
		for i := 0; i < m; i++ {
			fmt.Scan(&a, &b, &f)
			a--
			b--
			pointMap[a] = append(pointMap[a], Point{NextPoint: b, Fee: f})
			pointMap[b] = append(pointMap[b], Point{NextPoint: a, Fee: f})
		}
		pq := make(PriorityQueueNode, 0, m)
		start := Node{NowPosition: s, DiscountTicketTCount: c, Amount: 0}
		heap.Push(&pq, &start)
		memo := make(map[Memo]struct{})
		for len(pq) != 0 {
			now := heap.Pop(&pq).(*Node)
			if now.NowPosition == d {
				fmt.Println(now.Amount)
				break
			}
			memo[Memo{NowPoint: now.NowPosition, DiscountTicketTCount: now.DiscountTicketTCount}] = struct{}{}
			for _, v := range pointMap[now.NowPosition] {
				next := &Node{v.NextPoint, now.DiscountTicketTCount, now.Amount + v.Fee}
				if _, ok := memo[Memo{NowPoint: v.NextPoint, DiscountTicketTCount: now.DiscountTicketTCount}]; !ok {
					heap.Push(&pq, next)
				}
				if now.DiscountTicketTCount > 0 {
					next = &Node{v.NextPoint, now.DiscountTicketTCount - 1, now.Amount + v.Fee/2}
					if _, ok := memo[Memo{NowPoint: v.NextPoint, DiscountTicketTCount: now.DiscountTicketTCount}]; !ok {
						heap.Push(&pq, next)
					}
				}
			}
		}
		runtime.GC()
	}
}

C++: #include <bits/stdc++.h>
using namespace std;

const double PI = acos(-1);
const double EPS = 1e-15;
using ll = long long;
using ull = unsigned long long;
const int inf = 2e9;
const ll INF = 2e18;
const ll MOD = 1e9+7;
const ll MOD1 = 998244353;
typedef pair<int,int> P;

#define REP(i,n) for (int i = 0; i < (n); i++)
#define sz(s) (s).size()
#define pb push_back
#define fi first
#define se second
#define mp make_pair

int main(){
  int c,n,m,s,d;
  while (cin >> c >> n >> m >> s >> d,c,n,m,s,d) {
    int dp[110][11];
    REP(i,110) REP(j,11) dp[i][j] = inf;
    s--;
    d--;
    vector<pair<int,int>> G[110];
    REP(i,m) {
      int a,b,f;
      cin >> a >> b >> f;
      a--;
      b--;
      G[a].pb({b,f});
      G[b].pb({a,f});
    }
    priority_queue<pair<int,pair<int,int>>,vector<pair<int,pair<int,int>>>,greater<pair<int,pair<int,int>>>> pq;
    dp[s][0] = 0;
    pq.push({0,{s,0}});
    while (!pq.empty()) {
      pair<int,pair<int,int>> tp = pq.top();
      //cout << tp.fi << " " << tp.se.fi << " " << tp.se.se << endl;
      pq.pop();
      int point = tp.se.fi;
      int ticket = tp.se.se;
      if (tp.fi > dp[point][ticket]) continue;
      //cout << "test" << endl;
      REP(i,sz(G[point])) {
        int next = G[point][i].fi;
        int cost = G[point][i].se;
        if (dp[point][ticket] + cost < dp[next][ticket]) {
          dp[next][ticket] = dp[point][ticket] + cost;
          pq.push({dp[next][ticket],{next,ticket}});
        }
        if (dp[point][ticket] + cost/2 < dp[next][ticket+1]) {
          dp[next][ticket+1] = dp[point][ticket] + cost/2;
          pq.push({dp[next][ticket+1],{next,ticket+1}});
        }
      }
    }
    cout << dp[d][c] << endl;
  }
  return 0;
}

C++: #include<bits/stdc++.h>
#define rep(i,n)for(int i=0;i<n;i++)
using namespace std;
typedef pair<int, int>P;

struct node {
	int first, second, c;
};
bool operator<(node a, node b) {
	return a.second > b.second;
}
vector<P>E[100];
int d[100];

int main() {
	int c, n, m, s, g;
	while (scanf("%d%d%d%d%d", &c, &n, &m, &s, &g), c) {
		s--; g--;
		rep(i, 100)E[i].clear();
		memset(d, 0x3f, sizeof(d));
		rep(i, m) {
			int a, b, f; scanf("%d%d%d", &a, &b, &f);
			a--; b--;
			E[a].push_back(P(b, f)); E[b].push_back(P(a, f));
		}
		priority_queue<node>que;
		que.push({ s,0,c });
		d[s] = 0;
		while (!que.empty()) {
			node p = que.top(); que.pop();
			if (d[p.first] < p.second)continue;
			for (P i : E[p.first]) {
				if (p.c&& d[i.first] > p.second + i.second / 2) {
					d[i.first] = p.second + i.second / 2;
					que.push({ i.first, d[i.first],p.c - 1 });
				}
				if (d[i.first] > p.second + i.second) {
					d[i.first] = p.second + i.second;
					que.push({ i.first, d[i.first],p.c });
				}
			}
		}
		printf("%d\n", d[g]);
	}
}

C++: #include <stdio.h>
#include <string.h>
#include <algorithm>
#include <iostream>
#include <math.h>
#include <assert.h>
#include <vector>
#include <queue>

using namespace std;
typedef long long ll;
typedef unsigned int uint;
typedef unsigned long long ull;
static const double EPS = 1e-9;
static const double PI = acos(-1.0);

#define REP(i, n) for (int i = 0; i < (int)(n); i++)
#define FOR(i, s, n) for (int i = (s); i < (int)(n); i++)
#define FOREQ(i, s, n) for (int i = (s); i <= (int)(n); i++)
#define FORIT(it, c) for (__typeof((c).begin())it = (c).begin(); it != (c).end(); it++)
#define MEMSET(v, h) memset((v), h, sizeof(v))

typedef int Weight;
struct Edge {
  int cnt;
  int src;
  int dest;
  Weight weight;
  Edge(int cnt, int src, int dest, Weight weight) : cnt(cnt), src(src), dest(dest), weight(weight) {;}
  bool operator<(const Edge &rhs) const {
    return weight > rhs.weight;
  }
};
typedef vector<Edge> Edges;
typedef vector<Edges> Graph;

int c, n, m, s, d;
bool visit[20][110];

int main() {
  while (scanf("%d %d %d %d %d", &c, &n, &m, &s, &d), c|n|m|s|d) {
    MEMSET(visit, false);
    s--; d--;
    Graph g(n);
    REP(i, m) {
      int f, t, cost;
      scanf("%d %d %d", &f, &t, &cost);
      f--; t--;
      g[f].push_back(Edge(0xdeadbeaf, 0xdeadbeaf, t, cost));
      g[t].push_back(Edge(0xdeadbeaf, 0xdeadbeaf, f, cost));
    }
    priority_queue<Edge> que;
    que.push(Edge(c, 0xdeadbeaf, s, 0));
    while (!que.empty()) {
      Edge e = que.top();
      que.pop();
      if (visit[e.cnt][e.dest]) { continue; }
      visit[e.cnt][e.dest] = true;
      if (e.dest == d) {
        printf("%d\n", e.weight);
        break;
      }
      FORIT(it, g[e.dest]) {
        if (e.cnt != 0) {
          int ncost = e.weight + it->weight / 2;
          que.push(Edge(e.cnt - 1, 0xdeadbeaf, it->dest, ncost));
        }
        int ncost = e.weight + it->weight;
        que.push(Edge(e.cnt, 0xdeadbeaf, it->dest, ncost));
      }
    }
  }
}