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 <algorithm>
using namespace std;
#define MAX 101
#define INF 9999999

int c,n,m,s,d,a,b,f,cost[MAX+1][MAX+1],dd[MAX+1][MAX+1];
bool used[MAX+1][MAX+1];

int dijkstra(int s,int d,int c){
    fill(dd[0],dd[MAX],INF);
    fill(used[0],used[MAX],false);
    
    dd[c][s-1] = 0;
    while(true){
        int Mini = -1 , Minj;
        
        for(int i = 0 ; i < n ; i++){
            for(int j = 0 ; j <= c ; j++){
                if((dd[j][i] < dd[Minj][Mini] || Mini == -1)&&!used[j][i]){
                    Mini = i;
                    Minj = j;
                }
            }
        }
        
        if(Mini == -1) break;
        used[Minj][Mini] = true;
        
        for(int i = 0 ; i < n ; i++){
            dd[Minj][i] = min(dd[Minj][i],dd[Minj][Mini]+cost[Mini][i]);
            if(Minj > 0) dd[Minj-1][i] = min(dd[Minj-1][i],dd[Minj][Mini]+cost[Mini][i]/2);
        }
    }
    
    int res = INF;
    for(int i = 0 ; i <= c ; i++){
        res = min(res,dd[i][d-1]);
    }
    
    return res;
}

int main(){
    while(cin >> c >> n >> m >> s >> d, c+n+m+s+d){
        fill(cost[0],cost[MAX],INF);
        for(int i = 0 ; i < m ; i++){
            cin >> a >> b >> f;
            cost[a-1][b-1] = f;
            cost[b-1][a-1] = f;
        }
        
        cout << dijkstra(s,d,c) << endl;
    }
    
    return 0;
}

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

class State{
public:
  int v, c, t;
  State(int _v, int  _c, int _t)
    :v(_v), c(_c), t(_t) {}
  bool operator < (const State& st) const{
    return this->c > st.c;
  }
};


int main(){

  const int INF = 1 << 27;
 
  int ticket, n, m, start, goal;
  while(cin >> ticket >> n >> m >> start >> goal){
    if((ticket|n|m|start|goal) == 0) break;
    --start;
    --goal;

    int s, dd, score;
    vector<vector<vector<int> > >cost(n, vector<vector<int> >(n, vector<int>(ticket +1, INF*2)));
    for(int i=0; i<m; i++){
      cin >> s >> dd >> score;
      --s;
      --dd;
      cost[s][dd][0] = cost[dd][s][0] = score;
      for(int j=1; j<ticket; j++) cost[s][dd][j] = cost[dd][s][j] = score;      
      //cout << cost[s][dd][0] << endl;
    }

    priority_queue<State> req;
    vector<vector<int> > d(n, vector<int>(ticket+1, INF));
    for(int i=0; i<=ticket; i++){
      d[start][i] = 0;
 
    }
    req.push(State(start, 0, ticket));

    while(! req.empty()){
      State st = req.top();
      req.pop();

      //cout << "v:" << st.v+1 <<" c:" << st.c << " t:" << st.t << endl;

      if(st.v == goal){
	   cout << st.c << endl;
	   break;
      }

      for(int i=0; i<n; i++){
	if(i != st.v){
	//use ticket
	if(st.t>0 && d[st.v][st.t] + cost[st.v][i][st.t-1]/2 < d[i][st.t-1]){
	  d[i][st.t-1] = st.c + cost[st.v][i][st.t-1]/2;
	  req.push(State(i, d[i][st.t-1], st.t-1));
	}
	//not use ticket
	if(d[st.v][st.t] + cost[st.v][i][st.t] < d[i][st.t]){
	  d[i][st.t] = st.c + cost[st.v][i][st.t];
	  req.push(State(i, d[i][st.t], st.t));
	}
	}
      }
	
      
    }
  }
  return 0;
}

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

using namespace std;
#define INF 99999999
typedef pair<int, int> P;
typedef pair<P, int> PP;
struct Edge
{
	int to;
	int cost;
};

void solve()
{
	int c, n, m, s, d;
	while(cin >> c >> n >> m >> s >> d, c || n || m || m || s)
	{
		vector<Edge> V[101];
		for(int i = 0; i < m; ++i)
		{
			int from, to, cost;
			cin >> from >> to >> cost;
			--from; --to;
			Edge e1 = {to, cost};
			Edge e2 = {from, cost};
			V[from].push_back(e1);
			V[to].push_back(e2);
		}
		vector< vector<int> > dist(n, vector<int>(c + 1));
		for(int i = 0; i < dist.size(); ++i)
		{
			for(int j = 0; j < dist[i].size(); ++j)
			{
				dist[i][j] = INF;
			}
		}
		priority_queue<PP, vector<PP>, greater<PP> > pq;
		--s;
		dist[s][0] = 0;
		pq.push(PP(P(0, s), 0));
		while(!pq.empty())
		{
			PP pp = pq.top();
			pq.pop();
			int v = pp.first.second;
			int ticket = pp.second;
			if(dist[v][ticket] < pp.first.first)
			{
				continue;
			}
			for(int i = 0; i < V[v].size(); ++i)
			{
				Edge e = V[v][i];
				if(dist[e.to][ticket] > pp.first.first + e.cost)
				{
					dist[e.to][ticket] = pp.first.first + e.cost;
					pq.push(PP(P(dist[e.to][ticket], e.to), ticket));
				}
				if(ticket < c && dist[e.to][ticket + 1] > pp.first.first + e.cost / 2)
				{
					dist[e.to][ticket + 1] = pp.first.first + e.cost / 2;
					pq.push(PP(P(dist[e.to][ticket + 1], e.to), ticket + 1));
				}
			}
		}
		int min_cost = INF;
		for(int i = 0; i <= c; ++i)
		{
			if(min_cost > dist[d - 1][i])
			{
				min_cost = dist[d - 1][i];
			}
		}
		cout << min_cost << endl;
	}
}

int main()
{
	solve();
	return(0);
}