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<stdio.h>
#include<string.h>
#include<utility>
#include<queue>
#include<algorithm>
using namespace std;
#define INF 1000000000
int C,N,M,S,D,g1[101][101],g2[101][101],s,t,c,d[11][101];
typedef struct P{int p,c,t;}P;
struct Order
{
	bool operator ()(P const& a, P const& b) const
	{
		return a.c>b.c;
	}
};

P tmp,tmp2;
priority_queue<P,vector<P>,Order>Q;
int main()
{
	for(;scanf("%d%d%d%d%d",&C,&N,&M,&S,&D),C;)
	{
		for(int i=0;i<=N;i++)
			for(int j=0;j<=N;j++)
				g1[i][j]=g2[i][j]=INF;
		for(int i=0;i<=C;i++)
			for(int j=0;j<=N;j++)
				d[i][j]=INF;
		for(int i=0;i<M;i++)
		{
			scanf("%d%d%d",&s,&t,&c);
			if(g1[s][t]>c)
			{
				g1[s][t]=g1[t][s]=c;
				g2[s][t]=g2[t][s]=c/2;
			}
		}
		d[C][S]=0;
		tmp.c=0;tmp.p=S;tmp.t=C;
		Q.push(tmp);
		for(;!Q.empty();)
		{
			tmp=Q.top(),Q.pop();
			for(int i=1;i<=N;i++)
			{
				int nc=tmp.c+g1[tmp.p][i];
				if(d[tmp.t][i]>nc)
				{
					tmp2.c=d[tmp.t][i]=nc;
					tmp2.p=i;
					tmp2.t=tmp.t;
					Q.push(tmp2);
				}
				nc=tmp.c+g2[tmp.p][i];
				if(tmp.t>0&&d[tmp.t-1][i]>nc)
				{
					tmp2.c=d[tmp.t-1][i]=min(d[tmp.t][i],nc);
					tmp2.p=i;
					tmp2.t=tmp.t-1;
					Q.push(tmp2);
				}
			}
		}
		printf("%d\n",d[0][D]);
	}
}

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;
	}
}

C++: #include<iostream>
#include<map>
#include<queue>
#include<vector>
using namespace std;

#define N 100
#define C 50
#define INF 1000000007
#define rep(i, n) for(int i=0; i<n; ++i)

struct Edge {
	int to, cost;
};

typedef pair<int, int> P;
typedef pair<int, P> IP;

typedef vector<Edge> Graph;

Graph g[N];

int dist[N][C];
int n, c;
int dijkstra(int s, int t) {
	priority_queue<IP, vector<IP>, greater<IP> > q;
	rep(i, n) rep(j, c+1) dist[i][j] = INF;
	dist[s][0] = 0;
	q.push(IP(0, P(s, 0)));
	while(!q.empty()) {
		int cost = q.top().first, u = q.top().second.first;
		int p = q.top().second.second; q.pop();
		if(dist[u][p] < cost) continue;
		rep(i, g[u].size()) {
			Edge &e = g[u][i];
			if(dist[u][p] + e.cost < dist[e.to][p]) {
				dist[e.to][p] = dist[u][p] + e.cost;
				q.push(IP(dist[e.to][p], P(e.to, p)));
			}
			if(p < c && dist[u][p] + (e.cost / 2) < dist[e.to][p+1]) {
				dist[e.to][p+1] = dist[u][p] + (e.cost / 2);
				q.push(IP(dist[e.to][p+1], P(e.to, p+1)));
			}
		}
	}
	return dist[t][c];
}


int main() {
	int m, s, d;
	while(cin >> c >> n >> m >> s >> d && c && n && m && s && d) {
		--s; --d;
		rep(i, n) g[i].clear();
		rep(i, m) {
			int a, b, f;
			cin >> a >> b >> f; --a; --b;
			g[a].push_back((Edge){b, f});
			g[b].push_back((Edge){a, f});
		}
		cout << dijkstra(s, d) << endl;
	}
	return 0;
}

C++: #include <iostream>
#include <queue>
#include <array>
#include <vector>

using namespace std;
#define loop(i,a,b) for(int i=(a); i<(int)(b); i++)
#define rep(i,b) loop(i,0,b)

struct edge {
    int to,cost;
};
struct state {
    int v,d;
    bool operator<(const state& s) const {
        return d>s.d;
    }
};

vector<vector<edge>> G;
array<array<int,11>,101> dp;
priority_queue<state> q;
int c,n,m,s,d;

int main(){
    while(cin>>c>>n>>m>>s>>d, c||n||m||s||d){
        G=vector<vector<edge>>(n+1);
        rep(i,m){
            int f,t,c; cin>>f>>t>>c;
            G[f].push_back({t,c});
            G[t].push_back({f,c});
        }
        rep(i,c+1){
            dp[i].fill(1<<30);
            dp[i][s]=0;
            priority_queue<state>().swap(q);
            q.push({s,0});
            while(q.size()){
                state sta=q.top(); q.pop();
                if(dp[i][sta.v]<sta.d) continue;
                for(edge& e:G[sta.v]){
                    int t;
                    if(i==0) t=dp[0][sta.v]+e.cost;
                    else t=min(dp[i][sta.v]+e.cost,
                               dp[i-1][sta.v]+e.cost/2);
                    if(dp[i][e.to]>t){
                        dp[i][e.to]=t;
                        q.push({e.to,t});
                    }
                }
            }
        }
        cout<<dp[c][d]<<endl;
    }
}