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>
using namespace std;
#include<vector>
#include<queue>
//#include<math.h>
struct crq{
	int cost;
	int ticket;
	int now;

	bool operator > (const crq& p) const{
	return cost > p.cost;
	}
};//cost root que
struct root{
	int s;
	int g;
	int cost;
};




int c;
int n;
int m;
int s;
int d;
int ans;
bool townSearched[100];
int townMin[100][11];

int main(){
	while(cin>>c>>n>>m>>s>>d, c|n|m|s|d){
		vector<root> vr;
		ans=0;
		priority_queue<crq,vector<crq>,greater<crq>> q;
		while(!q.empty())q.pop();
		for(int  i=0;i<100;i++){
			townSearched[i]=false;
			for(int  j=0;j<11;j++)townMin[i][j]=1e8;
		}
		for(int i=0;i<m;i++){
			root r;
			cin>>r.s;
			r.s--;
			cin>>r.g;
			r.g--;
			cin>>r.cost;
			vr.push_back(r);
		}
		townMin[s-1][c]=0;
		crq start;
		start.cost=0;
		start.ticket=c;
		start.now=s-1;

		q.push(start);
		while(1){
			crq crq2=q.top();q.pop();
			if(crq2.now==d-1){
				ans=crq2.cost;
				break;
			}
			

			for(int i=0;i<m;i++){
				if(vr.at(i).s==crq2.now){
					if(!townSearched[vr.at(i).g]&&townMin[vr.at(i).g][crq2.ticket]>crq2.cost+vr.at(i).cost){
						crq add;
						add.cost=crq2.cost+vr.at(i).cost;
						add.ticket=crq2.ticket;
						add.now=vr.at(i).g;
						townMin[vr.at(i).g][crq2.ticket]=crq2.cost+vr.at(i).cost;
						q.push(add);
					}

					if(!townSearched[vr.at(i).g]&&crq2.ticket>0&&townMin[vr.at(i).g][crq2.ticket-1]>crq2.cost+vr.at(i).cost/2){
						crq add;
						add.cost=crq2.cost+vr.at(i).cost/2;
						add.ticket=crq2.ticket-1;
						add.now=vr.at(i).g;
						townMin[vr.at(i).g][crq2.ticket]=crq2.cost+vr.at(i).cost/2;
						q.push(add);
					}

				}
				if(vr.at(i).g==crq2.now){
					if(!townSearched[vr.at(i).s]&&townMin[vr.at(i).s][crq2.ticket]>crq2.cost+vr.at(i).cost){
						crq add;
						add.cost=crq2.cost+vr.at(i).cost;
						add.ticket=crq2.ticket;
						add.now=vr.at(i).s;
						townMin[vr.at(i).s][crq2.ticket]=crq2.cost+vr.at(i).cost;
						q.push(add);
					}

					if(!townSearched[vr.at(i).s]&&crq2.ticket>0&&townMin[vr.at(i).s][crq2.ticket-1]>crq2.cost+vr.at(i).cost/2){
						crq add;
						add.cost=crq2.cost+vr.at(i).cost/2;
						add.ticket=crq2.ticket-1;
						add.now=vr.at(i).s;
						townMin[vr.at(i).s][crq2.ticket]=crq2.cost+vr.at(i).cost/2;
						q.push(add);
					}

				}
			}
			townSearched[crq2.now]=true;
		}
		cout<<ans<<endl;
	}
	return 0;
}

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

#define INFTY 1<<30
#define N 101
#define C 11
#define CONNECTED 1
#define IN_QUEUE 1

using namespace std;

int cost[N][C];
bool vis[N][C];
int W[N][N];
int G[N][N];

class Node{
public:
	Node():id(0),cost(INFTY),c(0){}
	int id;
	int cost;
	int c;
	bool operator>(const Node &t)const{return this->cost > t.cost;}
};

void Dijkstra( Node s ){
	priority_queue<Node,vector<Node>,greater<Node>> pq;

	pq.push( s );

	while( !pq.empty() ){
		Node p = pq.top();

		pq.pop();

		if( vis[p.id][p.c] )
			continue;
		vis[p.id][p.c] = true;
		cost[p.id][p.c] = min( cost[p.id][p.c], p.cost );

		for(int i = 0; i < N; ++i){
			if( G[p.id][i] == CONNECTED ){
				Node np;

				np.id = i;
				np.cost = cost[p.id][p.c] + W[p.id][i];
				np.c = p.c;
				pq.push( np );
				if( p.c > 0 ){
					np.cost = cost[p.id][p.c] + (W[p.id][i]/2);
					np.c = p.c - 1;
					pq.push( np );
				}
			}
		}
	}
}
void ResetGraph(){
	for(int i = 0; i < N; ++i){
		for(int j = 0; j < C; ++j){
			cost[i][j] = INFTY;
			vis[i][j] = false;
		}
		for(int j = 0; j < N; ++j){
			G[i][j] = 0;
			W[i][j] = 0;
		}
	}
}
int main(){
	while( true ){
		int c, n, m, s, d;
		int ans = INFTY;
		Node start;
		
		cin >> c >> n >> m >> s >> d;
		if( !(c||n||m||s||d) )
			break;

		ResetGraph();
		for(int i = 0; i < m; ++i){
			int a, b, f;

			cin >> a >> b >> f;
			G[a][b] = G[b][a] = CONNECTED;
			W[a][b] = W[b][a] = f;
		}
		start.id = s;
		start.cost = 0;
		start.c = c;

		Dijkstra( start );

		for(int i = 0; i < C; ++i){
			ans = min(ans, cost[d][i]);
		}
		cout << ans << '\n';
	}
	return 0;
}