Go: package main

import (
	"bufio"
	"fmt"
	"math"
	"os"
	"strconv"
	"strings"
)

var scanner = bufio.NewScanner(os.Stdin)

const INF = 0x7FFFFFFF

var pass [][]int

func main() {
	for scanner.Scan() {
		pass = make([][]int, 200)
		for i := range pass {
			pass[i] = make([]int, 200)
		}
		buf := strings.Split(scanner.Text(), " ")
		c, _ := strconv.Atoi(buf[0])
		n, _ := strconv.Atoi(buf[1])
		m, _ := strconv.Atoi(buf[2])
		s, _ := strconv.Atoi(buf[3])
		d, _ := strconv.Atoi(buf[4])
		if c == 0 && n == 0 && m == 0 && s == 0 && d == 0 {
			break
		}
		s--
		d--
		for i := 0; i < 200; i++ {
			for j := 0; j < 200; j++ {
				pass[i][j] = INF
			}
		}
		for i := 0; i < 200; i++ {
			pass[i][i] = 0
		}
		for i := 0; i < m; i++ {
			scanner.Scan()
			buf_ := strings.Split(scanner.Text(), " ")
			a, _ := strconv.Atoi(buf_[0])
			b, _ := strconv.Atoi(buf_[1])
			f, _ := strconv.Atoi(buf_[2])
			a--
			b--
			pass[a][b] = f
			pass[b][a] = f
		}
		fmt.Println(dijkstra(s, d, c, n))
	}
}

func dijkstra(s, g, c, n int) float64 {
	d := make([][]float64, 200)
	used := make([][]bool, 200)
	for i := 0; i < 200; i++ {
		d[i] = make([]float64, 20)
		used[i] = make([]bool, 20)
	}
	for i := range d {
		for j := range d[i] {
			d[i][j] = INF
		}
	}
	d[s][c] = 0
	for {
		v := -1
		w := -1
		for u := 0; u < n; u++ {
			for i := 0; i < c+1; i++ {
				if !used[u][i] && (v == -1 || d[u][i] < d[v][w]) {
					v = u
					w = i
				}
			}
		}
		if v == -1 {
			break
		}
		used[v][w] = true
		for u := 0; u < n; u++ {
			d[u][w] = math.Min(d[u][w], d[v][w]+float64(pass[v][u]))
			if w-1 >= 0 && pass[v][u] != INF {
				d[u][w-1] = math.Min(d[u][w-1], d[v][w]+(float64(pass[v][u]/2.0)))
			}
		}
	}
	ret := float64(INF)
	for i := 0; i < c+1; i++ {
		ret = math.Min(ret, d[g][i])
	}
	return ret
}

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);
  for(int i = 0; i < coupon+1; ++i){
    for(int j = 0; j < graph.size(); ++j){
      visited[i][j] = false;
    }
  }
  while(!pq.empty()){
    state cur = pq.top(); pq.pop();
    //cout << cur.station << ": " << cur.cost << ": " << cur.coupon << endl;
    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 <stdio.h>
#include <cmath>
#include <algorithm>
#include <stack>
#include <queue>
#include <vector>
typedef long long int ll;

using namespace std;

int minimum,min_past_num,num_ticket,num_town,m,start,goal,costTable[101][101];


struct Info{
    Info(){
        current_town = 0;
        index = 0;
    }
    bool visited[102];
    int current_town,index,costs[102],visited_town[101];

};

void func(Info info){

    int sum = 0,limit;

    if(info.current_town == goal || (info.index >= min_past_num-2 && minimum != 2000000000))
    {

    	limit = min(num_ticket,info.index);

    	for(int i = 0; i < limit; i++){
    		sum += info.costs[i]/2;
    	}

    	for(int i = limit; i < info.index; i++){
    		sum += info.costs[i];
    	}

		if(info.current_town == goal){
			if(minimum > sum){
				minimum = sum;
				min_past_num = info.index;
			}
			return;
		}else{
			if(sum >= minimum){
				return;
			}
		}

    }

    int calc;
    for(int i = 1; i <= num_town; i++){
        if(costTable[info.current_town][i] != -1 && info.visited[i] == false){
            Info new_info;
            for(int k = 1; k <= num_town; k++)new_info.visited[k] = info.visited[k];
            new_info.visited[i] = true;
            new_info.current_town = i;

            if(costTable[info.current_town][i] > info.costs[0]){
            	new_info.costs[0] = costTable[info.current_town][i];
            	for(int k = 1; k <= info.index; k++){
            		new_info.costs[k] = info.costs[k-1];
            	}
            }else if(costTable[info.current_town][i] <= info.costs[info.index-1]){
            	for(int k = 0; k < info.index; k++){
            		new_info.costs[k] = info.costs[k];
            	}
            	new_info.costs[info.index] = costTable[info.current_town][i];
            }else{
            	for(calc = 0; info.costs[calc] >= costTable[info.current_town][i];calc++)new_info.costs[calc] = info.costs[calc];
				new_info.costs[calc] = costTable[info.current_town][i];
				calc++;
				for(;calc-1 < info.index;calc++)new_info.costs[calc] = info.costs[calc-1];
            }
            new_info.index = info.index+1;
            func(new_info);

        }
    }
}

int main(){

    int from,to,fee;

    while(true){
        scanf("%d %d %d %d %d",&num_ticket,&num_town,&m,&start,&goal);
        if(num_ticket == 0 && num_town == 0 && m == 0 && start == 0 && goal == 0)break;

        minimum = 2000000000;
        min_past_num = 101;

        for(int i = 1; i <= num_town; i++){
            for(int k = 1; k <= num_town; k++)costTable[i][k] = -1;
        }

        for(int i = 0; i < m; i++){
            scanf("%d %d %d",&from,&to,&fee);
            costTable[from][to] = fee;
            costTable[to][from] = fee;
        }

        Info info;
        for(int i = 1; i <= num_town;i++)info.visited[i] = false;

        info.current_town = start;
        info.visited[start] = true;

        func(info);

        printf("%d\n",minimum);
    }


    return 0;
}