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 <string>
#include <sstream>
#include <algorithm>
#include <vector>
#include <utility>
#include <functional>
#include <stack>
#include <queue>
#include <map>
#include <set>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <cmath>
#include <deque>
 
using namespace std;
 
#define rep(i,n) REP(i,0,n)
#define REP(i,s,e) for(int i=(s); i<(int)(e); i++)
#define pb push_back
#define mp make_pair
#define all(r) r.begin(),r.end()
#define fi first
#define se second
#define println(X) cout<<X<<endl;
#define DBG(X) cout<<#X<<" : "<<X<<endl;
 
 
typedef long long ll;
typedef vector<int> vi;
typedef vector<vi> vii;
typedef vector<ll> vl;
typedef vector<vl> vll;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
typedef pair<int, pii> pp;

const int INF = 1e9;

double EPS = 1e-10;


int c, n, m, s, g;



const int MAX_V = 510;

int d[MAX_V][MAX_V][15];
int connect[MAX_V][MAX_V];
int V;
 
void warshall_floyd_init(){
	for(int i = 0; i < V; i++){
		for(int j = 0; j < V; j++){
			for(int k = 0; k <= c; k++){
				if(i == j) d[i][i][k] = 0;
				else d[i][j][k] = INF;
			}
			connect[i][j] = 0;
		}
	}
}

void warshall_floyd() {
				for(int l = c; l>=0; l--){
				//for(int l = 0; l <= c; l++){
	for (int k = 0; k < V; k++) {
		for (int i = 0; i < V; i++) {
			for (int j = 0; j < V; j++) {
					d[i][j][l] = min({d[i][j][l], d[i][k][l] + d[k][j][c], d[i][k][c] + d[k][j][l]});
					if(l>0 && connect[k][j] > 0){
						d[i][j][l-1]=min(d[i][j][l-1], d[i][k][l]+connect[k][j]/2);
						//printf(" %d (%d -> %d -> %d), %d %d\n", l, i, k, j, d[i][j][l-1], d[i][k][l]+connect[k][j]/2);
					}
				}
			}
		}
	}
}
int main(){
	int a, b, f;
	int ans;
	while(cin>>c>>n>>m>>s>>g){
		if(c == 0 && n == 0 && m == 0 && s == 0 && g == 0) break;
		s--; g--;
		V = n;
		warshall_floyd_init();
		//cout<<d[0][2][0]<<endl;
		for(int i = 0; i < m; i++){
			cin>>a>>b>>f;
			//f/=10;
			a--; b--;
			//d[a][b][c] = d[b][a][c] = f;
			d[a][b][c] = min(d[a][b][c], f);
			d[b][a][c] = min(d[b][a][c], f);
			connect[a][b] = connect[b][a] = f;	
		}
		warshall_floyd();
		int ans = INF;
		for(int i = 0; i <= c; i++) ans = min(ans, d[s][g][i]);
		cout<<ans<<endl;
		//cout<<" "<<d[4][5][2]<<endl;
	}
	
}

C++: //Solution for aoj:0212 Highway Express Bus
#include<iostream>
#include<algorithm>
#include<vector>
#include<queue>
#include<functional>
using namespace std;
typedef pair<int, int>P;


struct S {
	int cost, to, num;
	S(int c, int t, int n) : cost(c), to(t), num(n){}
	bool operator>(const S &s) const {
		return cost > s.cost;
	}
};

const int INF = 1 << 30;
int c, n, m, s, d, w;
int tocost[101][11];
vector<P> town[501];
priority_queue<S, vector<S>, greater<S> > pq;


void dijkstra(){
	while (!pq.empty()){
		S a = pq.top();
		pq.pop();
		for (int i = 0; i < town[a.to].size(); i++){
			int tt = town[a.to][i].first, cc = town[a.to][i].second;
			if (tocost[tt][a.num] > cc + a.cost){
				tocost[tt][a.num] = cc + a.cost;
				pq.push({ cc + a.cost, tt, a.num });
			}
			if (a.num&&tocost[tt][a.num-1] > cc/2 + a.cost){
				tocost[tt][a.num-1] = cc/2 + a.cost;
				pq.push({ cc/2 + a.cost, tt, a.num-1 });
			}
		}
	}
}
	int main(){
		while (cin >> c >> n >> m >> s >> d&&c){
			for (int i = 0; i < 101; i++)
				fill(tocost[i], tocost[i] + 11, INF);
			fill(tocost[s], tocost[s] + 11, 0);
			while (pq.size())
				pq.pop();
			for (int i = 0; i < n; i++)
					town[i].erase(town[i].begin(),town[i].end());
			for (int i = 0; i < m; i++){
				int a, b, c;
				cin >> a >> b >> c;
				town[a].push_back({ b, c });
				town[b].push_back({ a, c });
			}
			pq.push({ 0, s, c });
			dijkstra();
			cout << tocost[d][0] << endl;
		}
	}

C++: #include <set>
#include <map>
#include <list>
#include <queue>
#include <stack>
#include <cmath>
#include <ctype.h>
#include <ctime>
#include <cstdio>
#include <vector>
#include <string>
#include <bitset>
#include <cctype>
#include <cstdlib>
#include <cstring>
#include <utility>
#include <numeric>
#include <complex>
#include <sstream>
#include <fstream>
#include <iomanip>
#include <cassert>
#include <iostream>
#include <iterator>
#include <algorithm>

using namespace std;

//4方向ベクトル→↑←↓
int dx[] ={1,0,-1,0};
int dy[] ={0,-1,0,1};
const int MAX_V =100;

int c,n,m,d;//割引券,街の数,路線の数,出発地,目的地
int a,b,f;//バスの始点、終点,料金
int cd[11][MAX_V];
int used[MAX_V];
int cost[MAX_V][MAX_V];
const int INF =10000000;
int mv;
int max1,max2;
int max1V,max2V;
void dijkstra(int s){
  for(int i = 0;i <=c;i++){
    for(int j = 0;j <n;j++){
      if(j !=s)
	cd[i][j] =INF;
      else
	cd[i][s] =0;
    }
  }
  int v;
  for(int k = 0;k <=c;k++){
    fill(used,used+MAX_V,-1);
    while(true){
      v = -1;
    for(int u = 0;u <n;u++){
      if(used[u] ==-1&&(v ==-1||cd[k][u]<cd[k][v]))
	v =u;
    }
    if(v ==-1)
      break;
    used[v] =1;
   
    for(int u = 0;u <n;u++){
      if(used[u] ==-1){
      if(k ==0){
	cd[k][u] =min(cd[k][u],cd[k][v]+cost[v][u]);
      }
      else{
	cd[k][u] = min(cd[k][u],min(cd[k][v]+cost[v][u],cd[k-1][v]+cost[v][u]/2));
      }
      }
    }
    }
  }
}
int main()
{
  int s;
  while(cin >>c>>n>>m>>s>>d){
    if(c+n+m+s+d ==0)
      break;
  for(int i = 0;i <n;i++){
    for(int j = 0;j < n;j++){
      if(i !=j)
	cost[i][j] =INF;
      else
	cost[i][j] = 0;
    }
  }
  for(int i = 0;i < m;i++){
    cin >>a>>b>>f;
    cost[a-1][b-1] = f;
    cost[b-1][a-1] = f;
  }
  dijkstra(s-1);
  cout <<cd[c][d-1]<<endl;
  }
  return 0;
}