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 <cstdio>
#include <utility>
#include <queue>
#include <algorithm>
#define INF (1<<27)
#define rep(i,n)for(int i=0;i<n;i++)
using namespace std;
typedef pair<int,int> _P; //point chicket
typedef pair<int,_P> P; //cost _P
struct Edge {
	int to,cost;
	Edge(int _to,int _cost) {to=_to,cost=_cost;}
};
int dist[11][100];
vector<Edge> edges[100];
int main() {
	int c,n,m,s,d;
	while(scanf("%d %d %d %d %d",&c,&n,&m,&s,&d),c) {
		rep(i,n) edges[i].clear();
		rep(i,c+1) rep(j,n) dist[i][j]=INF;
		rep(i,m) {
			int a,b,f;
			scanf("%d %d %d",&a,&b,&f);
			edges[a-1].push_back(Edge(b-1,f));
			edges[b-1].push_back(Edge(a-1,f));
		}
		priority_queue<P,vector<P>,greater<P> > Q;
		Q.push(P(0,_P(s-1,c)));
		dist[c][s-1]=0;
		while(!Q.empty()) {
			P p=Q.top(); Q.pop();
			_P _p=p.second;
			if(dist[_p.second][_p.first]<p.first) continue;
			rep(i,edges[_p.first].size()) {
				if(dist[_p.second][edges[_p.first][i].to]>(p.first+edges[_p.first][i].cost)) {
					dist[_p.second][edges[_p.first][i].to]=(p.first+edges[_p.first][i].cost);
					Q.push(P(p.first+edges[_p.first][i].cost,_P(edges[_p.first][i].to,_p.second)));
				}
				if(_p.second>0&&(dist[_p.second-1][edges[_p.first][i].to]>(p.first+edges[_p.first][i].cost/2))) {
					dist[_p.second-1][edges[_p.first][i].to]=(p.first+edges[_p.first][i].cost/2);
					Q.push(P(p.first+edges[_p.first][i].cost/2,_P(edges[_p.first][i].to,_p.second-1)));
				}
			}
		}
		int sum=1<<30;
		rep(i,c+1)if(sum>dist[i][d-1])sum=dist[i][d-1];
		printf("%d\n",sum);
	}
}

C++: #include <stdio.h>
#include <cctype>
#include <limits.h>
#include <math.h>
#include <complex>
#include <bitset>
#include <vector>
#include <map>
#include <set>
#include <stack>
#include <queue>
#include <cstring>
#include <string>
#include <sstream>
#include <algorithm>
#include <iomanip>
#include <iostream>

#define VARIABLE(x) cerr << #x << "=" << x << endl
#define BINARY(x) static_cast<bitset<16> >(x);
#define rep(i,n) for(int i=0;i<(int)(n);i++)
#define REP(i,m,n) for (int i=m;i<(int)(n);i++)
#define if_range(x, y, w, h) if (0<=(int)(x) && (int)(x)<(int)(w) && 0<=(int)(y) && (int)(y)<(int)(h))

const int INF = 1e9;
const double EPS = 1e-8;
const double PI = 3.14159;
int dx[4]={0, 1, 0, -1}, dy[4]={-1, 0, 1, 0};
using namespace std;
typedef long long ll;
//typedef pair<int, int> P;
struct P {
	int x, y, n;
	P(int n, int x, int y):n(n), x(x), y(y){}
	P(){}
};

/** Problem0212 : Highway Express Bus **/
struct edge{
	int from, to, cost;
	edge(int f, int t, int c):from(f), to(t), cost(c){}
	edge(){}
};
vector<edge> G;

int main()
{
	int C, N, M, S, D;
	while (cin>>C>>N>>M>>S>>D, C) {
		S--, D--;
		G.clear();
		
		rep(i, M) {
			int a, b, f;
			cin>>a>>b>>f;
			a--, b--;
			G.push_back(edge(a, b, f));
			G.push_back(edge(b, a, f));
		}
		
		int d[100][11];
		fill(d[0], d[0]+100*11, INF);
		for (int i=0; i<=C; i++) d[S][i]=0;
		
		while (true) {
			bool update=false;
			
			for (int i=0; i<G.size(); i++) {
				edge e = G[i];
				for (int j=0; j<=C; j++) {
					if (d[e.to][j] > d[e.from][j] + e.cost) {
						d[e.to][j] = d[e.from][j] + e.cost;
						update = true;
					}
					
					
					if (j+1<=C) {
						if (d[e.to][j+1] > d[e.from][j]+e.cost/2) {
							d[e.to][j+1] = d[e.from][j]+e.cost/2;
							update = true;
						}
					}
				}
			}
			
			if (!update) break;
		}
		
		int ans = INF;
		for (int i=0; i<=C; i++) {
			ans = min(ans, d[D][i]);
		}
		cout << ans << endl;
	}
}