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 <stdio.h>
#include <iostream>
#include <vector>
#include <list>
#include <cmath>
#include <fstream>
#include <algorithm>
#include <string>
#include <queue>
#include <set>
#include <map>
#include <complex>
#include <iterator>
#include <cstdlib>
#include <sstream>

using namespace std;

#define EPS (1e-10)
#define EQ(a,b) (abs((a) - (b)) < EPS)
#define EQV(a,b) (EQ((a).real(),(b).real()) && EQ((a).imag(),(b).imag()))

typedef long long ll;

const int MAX_SIZE = 10000;

struct edge{
	int to;
	int cost;
	int kipKind;
};

// ツノツーツドツづ個暗環置
vector<edge> G[101][11];
int d[101][11];
const int INF = 1000000000;


class Situation{
public:
	Situation(double _cost,int _node,int _used){
		cost = _cost;
		node = _node;
		used = _used;
	}

	Situation();

	double cost;
	int node;
	int used;

	bool operator<(const Situation &sit)const{
		return sit.cost < (this->cost);
	}
};

void dijkstra(int s,int g,int c){
	priority_queue<Situation> que;

	for(int i = 0; i < 101; i++)
		fill(d[i],d[i]+11,INF);
	d[s][c] = 0;

	que.push(Situation(0,s,c));
	while(!que.empty()){
		Situation p = que.top();
		que.pop();
		int v = p.node;
		int used = p.used;
		if(d[v][used] < p.cost)
			continue;
		for(int i = 0; i < G[v][used].size(); i++){
			edge e = G[v][used][i];
			if(d[e.to][e.kipKind] > d[v][used]+e.cost){
				d[e.to][e.kipKind] = d[v][used]+e.cost;
				que.push(Situation(d[e.to][e.kipKind],e.to,e.kipKind));
			}
		}

	}
	

	int minCost = INF;

	for(int i = 0; i <= c; i++){
		minCost = min(minCost,d[g][i]);
	}
	if(minCost != INF)
		cout << minCost << endl;
	else
		cout << "Impossible" << endl;
}



int main(){

	int n,m,s,d,c;
	while(cin>>c>>n>>m>>s>>d&&!(c==0&&n==0&&m==0&&s==0&&d==0)){
		s--;
		d--;
		for(int i = 0; i < m; i++){
			int from,to,cost;
			cin>>from>>to>>cost;
			from--;
			to--;
			for(int j = 0; j <= c; j++){
				if(j-1>=0){
					edge e;
					e.cost=cost/2;
					e.to=to;
					e.kipKind=j-1;
					G[from][j].push_back(e);
					e.to=from;
					G[to][j].push_back(e);
				}
				edge e;
				e.cost=cost;
				e.to=to;
				e.kipKind=j;
				G[from][j].push_back(e);
				e.to=from;
				G[to][j].push_back(e);
			}
		}
		dijkstra(s,d,c);
		for(int i = 0; i < 101; i++)
			for(int j = 0; j < 11; j++)
				G[i][j].clear();
		//cout<<endl;
	}


	return 0;
}

C++: #include <iostream>
#include <vector>
#include <queue>
#include <map>
#include <cassert>
#include <algorithm>
using namespace std;
typedef pair<int, int> edge;
struct state{
  int cost, coupon, station;
  state(int cost_, int coupon_, int station_):cost(cost_), coupon(coupon_), station(station_){}
  bool operator< (const state &s) const{
    if(cost == s.cost){
      return coupon > s.coupon;
    }
    return cost > s.cost;
  }
};
int djikstra(vector<vector<edge> > graph, int start, int goal, int coupon){
  priority_queue<state> pq;
  pq.push(state(0, coupon, start));
  bool visited[coupon][graph.size()];
  fill_n((bool*)visited, (coupon+1) * graph.size(), false);
  return 0;
  while(!pq.empty()){
    state cur = pq.top(); pq.pop();
    if(visited[cur.coupon][cur.station]){
      continue;
    }
    if(cur.station == goal){
      return cur.cost;
    }
    visited[cur.coupon][cur.station] = true;
    for(int i = 0; i < graph[cur.station].size(); ++i){
      int to = graph[cur.station][i].first;
      int c = graph[cur.station][i].second;
      if(cur.coupon > 0){
        pq.push(state(cur.cost+c/2, cur.coupon-1, to));
      }
      pq.push(state(cur.cost+c, cur.coupon, to));
    }
  }
  //assert(false);
  return -1;
}
int main(){
  int c, n, m, s, d;
  while(true){    
    cin >> c >> n >> m >> s >> d;
    if((c|n|m|s|d) == 0){
      break;
    }
    vector<vector<edge> > graph(n+1, vector<edge>());
    for(int i = 0; i < m; ++i){
      int a, b, f;
      cin >> a >> b >> f;
      graph[a].push_back(make_pair(b, f));
      graph[b].push_back(make_pair(a, f));
    }
    cout << djikstra(graph, s, d, c) << endl;
  }
  return 0;
}

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

#define reep(i,n,m) for(int i=(n);i<(m);i++)
#define rep(i,n) reep(i,0,n)

using namespace std;

class Edge{
public:
    int to;
    int cost;
    Edge(int to,int cost):to(to),cost(cost){}
};

class Node{
public:
    int distance;
    int num;
    int ticket;
    Node(){}
    Node(int distance, int num,int ticket):distance(distance),num(num),ticket(ticket){}
    bool operator<(const Node &b)const{
        return distance > b.distance;
    }
};

vector<Edge> edge[101];
bool flg[101][11];

int c,n,m,s,d;

int solve(){

    priority_queue<Node> Q;
    Q.push(Node(0,s,0));
    int ans = 1000000;
    while(!Q.empty()){
        Node node = Q.top();Q.pop();
        if(flg[node.num][node.ticket]){
            continue;
        }
        flg[node.num][node.ticket] = true;
        //printf("num->%d cost->%d ticket->%d\n",node.num,node.distance,node.ticket);
        if(node.num == d){
            ans = min(ans,node.distance);
        }

        rep(i,edge[node.num].size()){
            Edge e = edge[node.num][i];
            int cost = node.distance + e.cost;
            Q.push(Node(cost,e.to,node.ticket));
            if(node.ticket < c){
                int cost = node.distance + e.cost/2;
                Q.push(Node(cost,e.to,node.ticket+1));
            }
        }
    }
    return ans;
}



void init(){
    rep(i,101){
        edge[i].clear();
        rep(k,11){
            flg[i][k] = 0;
        }
    }
}

int main(){

    while(cin >> c >> n >> m >> s >> d,!m==0){
        init();
        rep(i,m){
            int a,b,c;
            cin >> a >> b >> c;
            edge[a].push_back(Edge(b,c));
            edge[b].push_back(Edge(a,c));
        }
        cout << solve() << endl;
    }
}