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
}

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)
					}
				}
			}
		}
	}
}

C++: #include<iostream>
#include<cstring>
#include<queue>
#include<vector>
using namespace std;

struct node{
  int cost;
  int c;
  int now;
  node(int C,int cc,int n):cost(C),c(cc),now(n){}
  bool operator >(const node &e) const{
    return cost > e.cost;
  }
};

int main()
{
  int c,n,m,s,d;

  for(;cin>>c>>n>>m>>s>>d,c;)
    {
      int edge[n][n];
      bool close[c+1][n];
      memset(edge,-1,sizeof(edge));
      memset(close,false,sizeof(close));      
      for(int i=0;i<m;i++)
	{
	  int a,b,f;
	  cin>>a>>b>>f;
	  a--;
	  b--;
	  edge[a][b]=f;
	  edge[b][a]=f;
	}
      s--;
      d--;
      priority_queue<node,vector<node>,greater<node> >qu;
      qu.push(node(0,c,s));
      while(!qu.empty())
	{
	  node tmp = qu.top();
	  //	  cout<<tmp.now<<" "<<tmp.cost<<" "<<tmp.c<<endl;
	  qu.pop();
	  close[tmp.c][tmp.now]=true;
	  if(tmp.now==d)
	    {
	      cout<<tmp.cost<<endl;
	      break;
	    }
	  for(int i=0;i<n;i++)
	    {
	      if(edge[tmp.now][i]!=-1)
		{
		  if(!close[tmp.c][i])
		    qu.push(node(edge[tmp.now][i]+tmp.cost,tmp.c,i));
		  if(tmp.c>0 && !close[tmp.c-1][i])
		    qu.push(node(edge[tmp.now][i]/2+tmp.cost,tmp.c-1,i));
		}
	    }
	}
    }

}

C++: #include<bits/stdc++.h>
using namespace std;
#define M 100000007
#define ff first.first
#define fs first.second;
typedef pair<int,int> P;
typedef pair<P,int> Pi;
int main(void){
	int c,n,m,s,d;
	while(1){
		cin>>c>>n>>m>>s>>d;
		if(n==0)break;
		vector<P> cost[n+1];
		for(int i=0;i<m;i++){
			int a,b,l;
			cin>>a>>b>>l;
			cost[a].push_back(P(b,l)); cost[b].push_back(P(a,l));
		}
		int leng[c+1][n+1];
		priority_queue<Pi> que;
		for(int i=0;i<=c;i++) fill(leng[i],leng[i]+n+1,M);
		leng[0][s]=0;
		que.push(Pi(P(0,0),s));
		while(!que.empty()){
			Pi p=que.top(); que.pop();
			int v=p.second,w=p.fs;
			if(leng[w][v]<p.ff) continue;
			for(int i=0;i<cost[v].size();i++){
				P x=cost[v][i];
				int t=leng[w][v]+x.second;
				if(leng[w][x.first]>t){
					leng[w][x.first]=t;
					que.push(Pi(P(t,w),x.first));
				}
				t-=x.second/2;
				if(w<c&&leng[w+1][x.first]>t){
					leng[w+1][x.first]=t;
					que.push(Pi(P(t,w+1),x.first));
				}
			}
		}
		cout<<leng[c][d]<<endl;
	}
	return 0;
}

C++: #include<iostream>
#include<map>
#include<cstdio>
#include<vector>
#include<algorithm>
#include<queue>
using namespace std;
typedef pair< int ,int > P;
typedef pair< int , P > road;
main(){
  while(1){
    int c,n,m,s,d;
    int a,b,f;
    vector< P > bus[120];
    int min_cost[120];
    queue< road > que;
    road r;
    P p;
    cin>>c>>n>>m>>s>>d;//c waribiki n mati m rosen s start d goal
    if(c==0&&n==0&&m==0&&s==0&&d==0)break;
    for(int i=1;i<=n;i++){
      min_cost[i]=1<<21;
    }
    for(int i=0;i<m;i++){
      cin>>a>>b>>f;
      p.first=b;
      p.second=f;
      bus[a].push_back(p);
      p.first=a;
      p.second=f;
      bus[b].push_back(p);
    }
    r.first=c;
    r.second.first=s;
    r.second.second=0;
    que.push(r);
    while(!que.empty()){
      road now=que.front();
      //cout<<"now="<<now.first<<" "<<now.second.first<<" "<<now.second.second<<endl;
      int size=bus[now.second.first].size();
      for(int i=0;i<size;i++){
	if(bus[now.second.first][i].second+now.second.second<min_cost[bus[now.second.first][i].first]){
	  min_cost[bus[now.second.first][i].first]=bus[now.second.first][i].second+now.second.second;
	  r.first=now.first;
	  r.second.first=bus[now.second.first][i].first;
	  r.second.second=bus[now.second.first][i].second+now.second.second;
	  que.push(r);
	}
	if(now.first!=0&&bus[now.second.first][i].second/2+now.second.second<min_cost[bus[now.second.first][i].first]){
	  min_cost[bus[now.second.first][i].first]=bus[now.second.first][i].second/2+now.second.second;
	  r.first=now.first-1;
	  r.second.first=bus[now.second.first][i].first;
	  r.second.second=bus[now.second.first][i].second/2+now.second.second;
	  que.push(r); 
	}
      }  
      que.pop();
    }
    while(!que.empty()){
      que.pop();
    }
    cout<<min_cost[d]<<endl;
  }
}