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<vector>
#include<queue>
#include<set>
#include<climits>
using namespace std;

struct Data{
  int id;
  int cost;
  int ticket;
};
bool operator<(Data a, Data b){
  return a.cost!=b.cost?a.cost>b.cost:(a.ticket!=b.ticket?a.ticket<b.ticket:a.id>b.id);
}
struct Data2{
  int id;
  int ticket;
};
bool operator<(Data2 a, Data2 b){
  return a.id!=b.id?a.id>b.id:a.ticket<b.ticket;
}

#define NONE INT_MAX

int Dijkstra(vector< vector<int> >A,int start,int goal,int ticket)
{
  vector<int>cost(A.size(),NONE);
  priority_queue<Data>q;
  set<Data2>used;

  Data node={start,0,ticket};
  q.push(node);
  cost[start]=0;

  while(q.size()){
    node=q.top();q.pop();
    if(node.id==goal)return node.cost;
    Data2 t={node.id,node.ticket};
    if(used.count(t))continue;
    used.insert(t);
    for(int i=0;i<A[node.id].size();i++){
      if(A[node.id][i]==NONE)continue;
      if(node.ticket){
	if(cost[i]>cost[node.id]+(A[node.id][i])/2){
	  Data next={i,cost[node.id]+(A[node.id][i])/2,node.ticket-1};
	  cost[i]=next.cost;
	  q.push(next);
	}
      }
      if(cost[i]<=cost[node.id]+A[node.id][i])continue;
      Data next={i,cost[node.id]+A[node.id][i],node.ticket};
      cost[i]=next.cost;
      q.push(next);
    }
  }
  return -1;
}

int main()
{
  int c,n,m,s,d;
  int a,b,f;
  while(cin>>c>>n>>m>>s>>d,c|n|m|s|d){
    s--;d--;
    vector< vector<int> >A(n,vector<int>(n,NONE));
    for(int i=0;i<m;i++){
      cin>>a>>b>>f;
      a--;b--;
      A[a][b]=A[b][a]=f;
    }
    cout<<Dijkstra(A,s,d,c)<<endl;
  }
}

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

using namespace std;

struct P {
	int from, cost, coupon;

	bool operator >(const P& p) const {
		return cost > p.cost;
	}
};

int ecost[101][101];
int ccost[101][11];
int c, n, m, s, d;
int i;

int main() {
	while(cin >> c >> n >> m >> s >> d, c|n|m|s|d) {
		fill_n((int *)ecost, 101*101, -1);
		fill_n((int *)ccost, 101*11, 1e8);
		for(i=0; i<11; i++) ccost[s][i] = 0;
		for(i=0; i<m; i++){
			int a, b, f;
			cin >> a >> b >> f;
			ecost[a][b] = f;
			ecost[b][a] = f;
		}
		priority_queue<P, vector<P>, greater<P>> q;
		q.push((P){s, 0, 0});
		int dcost;
		while(!q.empty()){
			P p = q.top(); q.pop();
			// cout << "pos=" << p.from << endl;
			// goal
			if(p.from == d) {
				dcost = p.cost;
				break;
			}
			//
			for(i=0; i<n+1; i++){ // i:to
				if(ecost[p.from][i] != -1){
					if(p.cost + ecost[p.from][i] < ccost[i][p.coupon]){
						q.push((P){i, p.cost + ecost[p.from][i], p.coupon});
					}
					if(p.coupon+1 <= c) {
						bool ifpush = true;
						for(int j=0; j <= p.coupon+1; j++) ifpush = ifpush && p.cost + ecost[p.from][i]/2 < ccost[i][j];
						if(ifpush) {
						// if(p.cost + ecost[p.from][i]/2 < ccost[i][p.coupon+1]){
							q.push((P){i, p.cost + ecost[p.from][i]/2, p.coupon+1});
						}
					}
				}
			}
		}
		cout << dcost << endl;
	}
	return 0;
}

C++: #include <iostream>
#include <queue>
#define INF (1e9)
#define N 101
#define C 11
using namespace std;
void dijkstra(int);
int M[N][N],d[N][C],c,n;
typedef struct data{
  int cost,pos,ticket;
  bool operator<(const data & right)const{
    return cost > right.cost;
  }
} data;
int main(){
  int m,s,id,a,b,f;
  while(1){
    cin >> c >> n >> m >> s >> id;
    if(c==0&&n==0&&m==0&&s==0&&id==0) break;
    for(int i=0;i<=n;i++)
      for(int j=0;j<=n;j++)
	M[i][j]=INF;
    for(int i=0;i<m;i++){
      cin >> a >> b >> f;
      M[a][b]=M[b][a]=f;
    }
    dijkstra(s);
    cout << d[id][c] << endl;
  }
  return 0;
}
void dijkstra(int s){
  priority_queue<data> q;
  for(int i=1;i<=n;i++)
    for(int j=0;j<=c;j++)
      d[i][j]=INF;
  d[s][0]=0;
  q.push((data){0,s,0});
  while(!q.empty()){
    data t=q.top();
    q.pop();
    int cost=t.cost,pos=t.pos,ticket=t.ticket;
    //    if(d[pos][ticket]>cost) continue;
    for(int i=1;i<=n;i++){
      if(d[i][ticket]>d[pos][ticket]+M[pos][i]){
	d[i][ticket]=d[pos][ticket]+M[pos][i];
	q.push((data){d[i][ticket],i,ticket});
      }
      if(ticket==c) continue;
      if(d[i][ticket+1]>d[pos][ticket]+M[pos][i]/2){
	d[i][ticket+1]=d[pos][ticket]+M[pos][i]/2;
	q.push((data){d[i][ticket+1],i,ticket+1});
      }
    }
  }
}

C++: #include<bits/stdc++.h>
#define F first
#define S second
#define INF 1<<28
using namespace std;
 
int c, n, s, d;
typedef pair < int, int > P;
typedef pair < int, P > PP;
vector < P > vec[111];
 
int solve(){
 
  int dist[111][11]; for(int i=0;i<111;i++)for(int j=0;j<11;j++) dist[i][j] = INF;
  priority_queue < PP, vector<PP>, greater<PP> > que;
 
  dist[s][c] = 0;
  que.push( PP(0, P(s, c)) ); //Now_cost, Now_node, Now_ticket
 
  while(!que.empty()){
    PP p = que.top(); que.pop();
    int cost = p.F, now = p.S.F, tic = p.S.S;
 
    //if(dist[now][tic] < cost) continue;
    for(int i=0;i<vec[now].size();i++){
      P to = vec[now][i];
      if(dist[to.S][tic] > dist[now][tic] + to.F){
	dist[to.S][tic] = dist[now][tic] + to.F;
	que.push( PP(dist[to.S][tic], P(to.S, tic)) );
      }
      if(tic && dist[to.S][tic-1] > dist[now][tic] + to.F/2){
	dist[to.S][tic-1] = dist[now][tic] + to.F/2;
	que.push( PP(dist[to.S][tic-1], P(to.S, tic-1)) );
      }
    }
  }
   
  int ans = INF;
  for(int i=0;i<=c;i++){ ans = min(ans, dist[d][i]); } //cout << ans << endl; }
  return dist[d][0];
}
 
int main(){
 
  int m, a, b, p;
 
   
  while(cin >> c >> n >> m >> s >> d){
    if((c|n|m|s|d) == 0) break;
    for(int i=0;i<111;i++) vec[i].clear();
    for(;m--;){
      cin >> a >> b >> p;
      vec[a].push_back(P(p, b)); //[now] P(cost, next);
      vec[b].push_back(P(p, a));
    }
     
    cout << solve() << endl;
  }
   
}