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;

const int INF = 1000000000;

int c, n, m, s, d;
int visited[100][11];
int edge[100][100];


void dfs(int p, int rem, int cost){
   if(visited[p][rem] < cost) return;
   visited[p][rem] = cost;
   if(p == d) return;
   for(int i=0;i<n;i++){
      if(edge[p][i] == INF) continue;
      if(rem > 0 ) dfs(i, rem-1, cost+(edge[p][i]/2));
      dfs(i, rem, cost+edge[p][i]);
   }
}

main(){
   while(cin >> c >> n >> m >> s >> d && (c || n || m || s || d)){
      fill(edge[0], edge[100], INF);
      fill(visited[0], visited[100], INF);
      --s; --d;
      for(int i=0;i<m;i++){
         int a, b, f;
         cin >> a >> b >> f;
         --a; --b;
         edge[a][b] = edge[b][a] = f;
      }
      dfs(s, c, 0);
      int ans = INF;
      for(int i=0;i<c;i++){
         ans = min(ans, visited[d][i]);
      }
      cout << ans << endl;
   }
   return 0;
}

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

#define INF 1010000000
#define rep(i,n) for(int i=0;i<n;i++)
#define reps(i,n) for(int i=1;i<=n;i++)
#define sint(i) scanf("%d",&i);
#define sintt(i,j) scanf("%d%d",&i,&j);
#define sinttt(i,j,k) scanf("%d%d%d",&i,&j,&k);

using namespace std;

class S{
	public:
	int p;
	int v;
	int n;
	
	S(int p,int v,int n):p(p),v(v),n(n){}
	
	bool operator<(const S&a)const{
		return v>a.v;
		return v==a.v ? v>a.v : n <a.n;
	}
};

int main(){
	while(1){
		int c,n,m,s,g;
		scanf("%d%d%d%d%d",&c,&n,&m,&s,&g);
		if(c==0&&n==0&&m==0&&s==0&&g==0)break;
		
		int root[101][101];
		rep(i,101)rep(j,101)root[i][j]=INF;
		
		rep(i,101)root[i][i]=0;
		
		rep(i,m){
			int a,b,d;
			sinttt(a,b,d);
			root[a][b]=d;
			root[b][a]=d;
		}
		
		priority_queue<S> qui;
		qui.push(S(s,0,0));
		int ans=0;
		
		int visit[101][11];
		rep(i,101)rep(j,11)visit[i][j]=0;
		
		while(1){
			if(qui.empty()==1){
				ans=-1;
				break;
			}
			
			S u=qui.top();qui.pop();
			if(visit[u.p][u.n]==1){continue;}
			
			//printf("%d %d %d\n",u.p,u.v,u.n);
			if(u.p==g){
				ans=u.v;
				break;
			}
			
			visit[u.p][u.n]=1;
			
			reps(i,n){
				if(root[u.p][i]!=INF){
						qui.push(S(i,u.v+root[u.p][i],u.n));
						
					if(visit[i][u.n+1]==0 && u.n+1 <= c){
						qui.push(S(i,u.v+root[u.p][i]/2,u.n+1));
					}
				}
			}
		}
		printf("%d\n",ans);
	}
}

C++: #include "bits/stdc++.h"
using namespace std;
using ll = long long; using pii = pair<int, int>;
const int MOD = (int)1e9 + 7, INF = (1 << 27); const ll INFLL = (1LL << 55);
#define FOR(i,a,b) for(int (i)=(a);i<(int)(b);i++)
#define rep(i,n) FOR(i,0,n)
template<typename T> void dbg(T x) { cout << x << "\n"; }
template<typename T, typename U> static void chmin(T &x, U y) { if (y < x) x = y; }
template<typename T, typename U> static void chmax(T &x, U y) { if (x < y) x = y; }


int n, m;

// O(n^2)
using Dist = int;
const int VMAX = 110;
Dist cost[VMAX][VMAX];
Dist d[12][VMAX];
void dijkstra(int s, int a) {
    d[a][s] = 0;
    vector<int> used(n, 0);
    while (1) {
        int v = -1;
        for (int to = 0; to < n; to++) {
            if (used[to]) continue;
            if (v == -1 || d[a][to] < d[a][v]) v = to;
        }
        if (v == -1) break;
        used[v] = 1;
        for (int to = 0; to < n; to++) {
            Dist nd = d[a][v] + cost[v][to];
            if (a > 0) chmin(nd, d[a - 1][v] + cost[v][to] / 2);
            if (nd < d[a][to]) d[a][to] = nd;
        }
    }
}

void init() {
    fill_n(*d, 12 * VMAX, INF);
    fill_n(*cost, VMAX * VMAX, INF);
}

int main() {
    int c, s, t;
    while (cin >> c >> n >> m >> s >> t, c) {
        init();
        s--; t--;
        rep(i, m) {
            int a, b, f; cin >> a >> b >> f;
            a--; b--;
            cost[a][b] = cost[b][a] = f;
        }
        rep(a, c + 1) dijkstra(s, a);
        cout << d[c][t] << "\n";
    }

    return 0;
}

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, ans;
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);
			tocost[s][c] = 0;
			ans = INF;
			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();
			for (int i = 0; i <= c; i++)
				ans = min(ans, tocost[d][i]);
			cout << ans << endl;
		}
		return 0;
	}