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>
using namespace std;

const int INF = 1 << 30;

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

int main()
{
  int c, n, m, s, d;
  while (cin >> c >> n >> m >> s >> d) {
    if ((c|n|m|s|d) == 0)
      break;

    --s;
    --d;
    vector<vector<int> > path(n, vector<int>(n, INF));
    for (int i = 0; i < m; ++i) {
      int a, b, f;
      cin >> a >> b >> f;
      --a;
      --b;
      path[a][b] = path[b][a] = f;
    }

    priority_queue<State> que;
    que.push(State(s, c, 0));
    vector<vector<int> > dp(n, vector<int>(c+1, INF));
    while (!que.empty()) {
      const State st = que.top();
      que.pop();

      if (st.v == d) {
	cout << st.f << endl;
	break;
      }

      if (dp[st.v][st.c] < st.f)
	continue;
      dp[st.v][st.c] = st.f;

      for (int i = 0; i < n; ++i) {
	if (path[st.v][i] == INF)
	  continue;

	if (st.c > 0) {
	  if (dp[i][st.c-1] > st.f + path[st.v][i]/2) {
	    dp[i][st.c-1] = st.f + path[st.v][i]/2;
	    que.push(State(i, st.c-1, dp[i][st.c-1]));
	  }
	}

	if (dp[i][st.c] > st.f + path[st.v][i]) {
	  dp[i][st.c] = st.f + path[st.v][i];
	  que.push(State(i, st.c, dp[i][st.c]));
	}
      }
    }

  }
  return 0;
}

C++: #include <bits/stdc++.h>
#define FOR(i,a,b) for(int i=(a);i<(b);i++)
#define RFOR(i,a,b) for(int i=(b) - 1;i>=(a);i--)
#define REP(i,n) for(int i=0;i<(n);i++)
#define RREP(i,n) for(int i=n-1;i>=0;i--)

#define PB push_back
#define INF INT_MAX/3
#define ALL(a) (a).begin(),(a).end()
#define RALL(a) (a).rbegin(),(a).rend()
#define CLR(a) memset(a,0,sizeof(a))

typedef long long int ll;

using namespace std;

int c,n,m,s,d;
int rosen[101][101] = {-1};
int saiki(int p,vector<int> st,vector<bool> &u){
    int ans = INF;
    if(p == d){
	sort(RALL(st));
	int tc = min(c,(int)(st.size()));
	REP(i,tc){
	    st[i] /= 2;
	}
	int sum = 0;
	REP(i,st.size()){
	    sum += st[i];
	}
	return sum;
    }
    FOR(i,1,n+1){
	if(!u[i] && rosen[p][i] > 0){
	    vector<int> temp = st;
	    vector<bool> utemp = u;
	    temp.PB(rosen[p][i]);
	    utemp[i] = true;
	    ans = min(ans,saiki(i,temp,utemp));
	}
    }
    return ans;
}

int main(){
    while(true){
	scanf("%d%d%d%d%d",&c,&n,&m,&s,&d);
	if(c==0&&n==0&&m==0&&s==0&&d==0) break;
	memset(rosen,-1,sizeof(rosen));
	REP(i,m){
	    int a,b,f;
	    cin >> a >> b >> f;
	    rosen[a][b] = f;
	    rosen[b][a] = f;
	}
	vector<bool>  used(n+1,false);
	vector<int> nanika;
	used[s] = true;
	cout << saiki(s, nanika ,used) << endl;
    }
    return 0;
}

C++: #include<iostream>
#include<iomanip>
#include<math.h>
#include<algorithm>
#include<string>
#include<vector>
#include<queue>
#include<stack>
#include<set>
#include<map>
#define REP(i, N) for(ll i = 0; i < N; ++i)
#define FOR(i, a, b) for(ll i = a; i < b; ++i)
#define ALL(a) (a).begin(),(a).end()
#define pb push_back
#define INF (long long)1000000000
#define MOD 1000000007
using namespace std;
typedef long long ll;
typedef pair<ll, ll> P;
int dx[4] = {1, 0, -1, 0};
int dy[4] = {0, 1, 0, -1};

int main(void) {
	while(true) {
		ll c, n, m, s, d;
		cin>>c>>n>>m>>s>>d;
		if(c == 0 && n == 0 && m == 0 && s == 0 && d == 0) break;
		--s;
		--d;
		vector<vector<P> > p(n);
		vector<vector<ll> > dir(n, vector<ll>(c + 1, INF * INF));
		REP(i, m) {
			int a, b, f;
			cin>>a>>b>>f;
			--a;
			--b;
			p[a].pb(P(b, f));
			p[b].pb(P(a, f));
		}
		priority_queue<pair<P, ll> > que;
		que.push(pair<P, ll>(P(0, s), c));
		dir[s][c] = 0;
		while(!que.empty()) {
			pair<P, ll> np = que.top();
			que.pop();
			if(dir[np.first.second][np.second] != np.first.first) continue;
			REP(i, p[np.first.second].size()) {
				if(dir[p[np.first.second][i].first][np.second] > dir[np.first.second][np.second] + p[np.first.second][i].second) {
					dir[p[np.first.second][i].first][np.second] = dir[np.first.second][np.second] + p[np.first.second][i].second;
					que.push(pair<P, ll>(P(dir[p[np.first.second][i].first][np.second], p[np.first.second][i].first), np.second));
				}
				if(np.second > 0 && dir[p[np.first.second][i].first][np.second - 1] > dir[np.first.second][np.second] + p[np.first.second][i].second / 2) {
					dir[p[np.first.second][i].first][np.second - 1] = dir[np.first.second][np.second] + p[np.first.second][i].second / 2;
					que.push(pair<P, ll>(P(dir[p[np.first.second][i].first][np.second - 1], p[np.first.second][i].first), np.second - 1));
				}
			}
		}
		ll res = INF * INF;
		REP(i, c + 1) {
			res = min(res, dir[d][i]);
		}
		cout<<res<<endl;
	}
}