Go: package main

import (
	"container/heap"
	"fmt"
)

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
}

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)
		}
		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)
		start := Node{NowPosition: s, DiscountTicketTCount: c, Amount: 0}
		heap.Push(&pq, &start)
		for len(pq) != 0 {
			now := heap.Pop(&pq).(*Node)
			if now.NowPosition == d {
				fmt.Println(now.Amount)
				break
			}
			for _, v := range pointMap[now.NowPosition] {
				next := &Node{v.NextPoint, now.DiscountTicketTCount, now.Amount + v.Fee}
				heap.Push(&pq, next)
				if now.DiscountTicketTCount > 0 {
					next = &Node{v.NextPoint, now.DiscountTicketTCount - 1, now.Amount + v.Fee/2}
					heap.Push(&pq, next)
				}
			}
		}
	}
}

C++: #include<iostream>
#include<cstdio>
#include<algorithm>
#include<queue>
#include<cstring>
#include<vector>
#include<string>
#define reep(a,s,d) for(int a=d;a<s;a++)
#define rep(a,s) reep(a,s,0)
using namespace std;
struct edge{
    int to,cost,tick;
    edge(int to,int cost,int tick):to(to),cost(cost),tick(tick){}
    edge(){}
};
bool operator<(const edge &a,const edge &b){
    return a.cost>b.cost;
}
int main(){
    int c,n,m,s,d;
    while(cin>>c>>n>>m>>s>>d,c){
        vector<edge> G[128];
        rep(i,m){
            int a,b,c;
            cin>>a>>b>>c;
            G[--a].push_back(edge(--b,c,0));
            G[b].push_back(edge(a,c,0));
        }
        bool vis[16][128];
        memset(vis,false,sizeof(vis));
        priority_queue<edge> Q;
        Q.push(edge(s-1,0,0));
        int ret=-1;
        while(!Q.empty()){
            edge n=Q.top();Q.pop();
            if(vis[n.tick][n.to])continue;
            vis[n.tick][n.to]=true;
            if(n.to==d-1){
                if(ret!=-1)ret=min(ret,n.cost);
                else ret=n.cost;
            }
            rep(i,G[n.to].size()){
                Q.push(edge(G[n.to][i].to,n.cost+G[n.to][i].cost,n.tick));
                if(n.tick<c){
                    Q.push(edge(G[n.to][i].to,n.cost+G[n.to][i].cost/2,n.tick+1));
                }
            }
        }
        cout<<ret<<endl;
    }
}

C++: #include<iostream>
#include<vector>
#include<algorithm>
#include<queue>
#include<climits>

using namespace std;

typedef pair<int,pair<int,int> >P;

struct Edge{
  int to,cost;
  Edge(int _to, int _cost):to(_to), cost(_cost){};
};

int minCost[101][11];
vector<Edge> edge[101];
static const int INF = 100000000;

int c,n,m,s,d;

int dijkstra(void){
  priority_queue<P, vector<P>, greater<P> >que;
  que.push(make_pair(0,make_pair(s,c)));

  for(int i=0;i<=n;i++)
    for(int j=0;j<=n;j++)
      minCost[i][j]=INF;

  while(!que.empty()){
    P p = que.top();
    que.pop();
    
    for(int i=0;i<edge[p.second.first].size();i++){
      Edge e = edge[p.second.first][i];
      if(p.first+e.cost < minCost[e.to][p.second.second]){
	minCost[e.to][p.second.second] = p.first+e.cost;
	que.push(make_pair(p.first+e.cost,make_pair(e.to,p.second.second)));
      }
    }
    
    if(p.second.second==0)continue;
    
    for(int j=0;j<edge[p.second.first].size();j++){
      Edge e = edge[p.second.first][j];
      if(p.first+e.cost/2 < minCost[e.to][p.second.second-1]){
	minCost[e.to][p.second.second-1] = p.first+e.cost/2;
	que.push(make_pair(p.first+e.cost/2,make_pair(e.to,p.second.second-1)));
      }
    }
  }

  return minCost[d][0];
}

int main(void){
  int a,b,f;

  while(cin >> c >> n >> m >> s >> d,c|n|m|s|d){

    for(int i=0;i<=n;i++)edge[i].clear();

    for(int i=0;i<m;i++){
      cin >> a >> b >> f;
      edge[a].push_back(Edge(b,f));
      edge[b].push_back(Edge(a,f));
    }

    cout << dijkstra() << endl;
  }

  return 0;
}

C++: #include <iostream>
#include <queue>
#include <functional>
#include <algorithm>
#include <cstring>
#include <vector>
#include <map>

const int MAX_V = 101;
const int INF = 0x3f3f3f3f;

//??? T???cap??????rev????????°???????????§?????£???????????????
struct Edge{
	int to;
	int cost;
	Edge(int to_, int cost_) :to(to_), cost(cost_){}
};

std::vector<Edge > G[MAX_V]; //??£??\?????????

int d[11][MAX_V]; //[?????¨???????????±??????????????°][?????????]
int pre[MAX_V];

void AddEdge(int from, int to, int cost){
	G[from].push_back(Edge(to, cost));
}

void ClearEdge(){
	for (int i = 0; i < MAX_V; ++i) G[i].clear();
	memset(d, 0, sizeof(d));
	memset(pre, -1, sizeof(pre));
}

void Dijkstra(int c, int s){
	typedef std::pair<int, int> P; //first:???????????¢, second:????????????

	std::priority_queue<P, std::vector<P>, std::greater<P> > q;
	std::fill(d[c], d[c] + MAX_V, INF);
	memset(pre, -1, sizeof(pre));
	d[c][s] = 0;
	q.push(P(0, s));

	while (!q.empty()){
		P p = q.top(); q.pop();
		int from = p.second;
		if (d[c][from] < p.first) continue;
		for (Edge e : G[from]){
			int dmin;
			if (c == 0)
				dmin = d[c][from] + e.cost;
			else
				dmin = std::min(d[c][from] + e.cost, d[c - 1][from] + e.cost / 2);

			if (d[c][e.to] > dmin){
				d[c][e.to] = dmin;
				q.push(P(d[c][e.to], e.to));
				pre[e.to] = from;
			}
		}
	}
}

std::vector<int> GetPath(int t){
	std::vector<int> path;
	for (; t != -1; t = pre[t]) path.push_back(t);
	std::reverse(path.begin(), path.end());

	return path;
}

using namespace std;

int main(void){
	int c, n, m, s, g;
	while (1){
		cin >> c >> n >> m >> s >> g;
		if (c == n && n == m && m == s && s == g && g == 0) return 0;
		int a, b, f;
		for (int i = 0; i < m; ++i){
			cin >> a >> b >> f;
			AddEdge(a, b, f);
			AddEdge(b, a, f);
		}
		for (int i = 0; i <= c; ++i){
			Dijkstra(i, s);
		}
		cout << d[c][g] << endl;
		ClearEdge();
	}
}

C++: #include<bits/stdc++.h>
#define MAX_V 101
using namespace std;

struct edge { 
  int to, cost;
  edge(){}
  edge(int to,int cost):to(to),cost(cost){};
};
typedef pair<int ,int> P;
const int INF = 1 << 30;
int V; //ノードの数
vector<edge> Graph[MAX_V];
int min_cost[11][MAX_V];

int c,m,s,d;
void Dijkstra(int s,int chip){ // s:スタートからの最小コストをmin_costに設定
  priority_queue<P,vector< P >, greater<P> > que;
  fill(min_cost[chip],min_cost[chip] + V,INF);
  min_cost[chip][s] = 0;
  que.push(P(0,s));
  
  while(!que.empty()){
    P p = que.top();que.pop();
    int now = p.second;
    int cost = p.first;
    if(min_cost[chip][now] < cost) continue;
    
    for(int i = 0; i < Graph[now].size(); i++){
      edge e = Graph[now][i];
      int a;
      if(chip == 0){
	a = min_cost[chip][now] + e.cost;
      }else{
	a = min(min_cost[chip][now] + e.cost, min_cost[chip-1][now] + e.cost / 2);
	if(min_cost[chip][e.to] > a){
	  min_cost[chip][e.to] = a;
	  que.push(P(min_cost[chip][e.to], e.to));
	}
      }
    }
  }
}

int main(){
  
  while(cin >> c >> V >> m >> s >> d && (c||V||m||s||d)){
    s--;
    d--;
    
    for(int i=0;i<m;i++){
      int a,b,f;
      cin>>a>>b>>f;
      a--;b--;
      Graph[a].push_back(edge(b,f));
      Graph[b].push_back(edge(a,f));
    }
    
    for(int i=0;i<=c;i++){
      Dijkstra(s,i);
    }

    cout<<min_cost[c][d]<<endl;
    
    for(int i=0;i<V;i++) Graph[i].clear();
  }
  return 0;
}