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 <bits/stdc++.h>
using namespace std;
#define FOR(i, s, n) for(int i = s; i < (int)n; i++)
#define per(i, n) for(int i = n; i >= 0; i--)
#define ROF(i, s, n) for(int i = s; i >= (int)n; i--)
#define FORIT(i, A) for (auto i : A)
#define PRINT(x) cout << (x) << "\n"
#define ALL(a) (a).begin(),(a).end()
#define RALL(a) (a).rbegin(), (a).rend()
#define MP make_pair
#define EACH(i, n) for (__typeof((n).begin()) i = (n).begin(); i != (n).end(); ++i)
#define SZ(a) int((a).size())
#define EXIST(s,e) ((s).find(e)!=(s).end())
#define SORT(c) sort((c).begin(),(c).end())
#define CLR(a) memset((a), 0 ,sizeof(a))
#define NCLR(a) memset((a), -1 ,sizeof(a))
#define dump(x) cout << #x << " = " << (x) << "\n";
#define debug(x) cout << #x << " = " << (x) << " (L" << __LINE__ << ")" << " " << __FILE__ << "\n";
#define sq(n) (n) * (n)
typedef vector<int> VI;
typedef vector<VI> VVI;
typedef vector<string> VS;
typedef pair<int, int> PII;
typedef long long LL;
typedef vector<LL> VLL;
typedef vector<VLL> VVLL;
typedef unsigned int uint;
typedef unsigned long long ull;
typedef priority_queue<int> maxpq;
typedef priority_queue< int, vector<int>, greater<int> > minpq;
static const double EPS = 1e-10;
static const double PI = acos( -1.0 );
static const int mod = 1000000007;
static const int INF = 1 << 25;
static const LL LL_INF = 1152921504606846976;
static const int dx[] = { -1, 0, 1, 0, 1, -1, 1, -1 };
static const int dy[] = { 0, -1, 0, 1, 1, 1, -1, -1 };



int c, n, m, s, d;
int dp[ 11 ][ 101 ];
static int _root[ 100 ][ 100 ];

int solve( int now, int can_use, set<int> p ) {
	p.insert( now );
	if ( now == d ) {
		return 0;
	}
	if ( dp[ can_use ][ now ] >= 0 ) {
		return dp[ can_use ][ now ];
	}
	int res = 1 << 30;
	for ( int i = 0; i < n; ++i ) {
		if ( p.count( i ) || _root[ now ][ i ] >= res ) {
			continue;
		}
		res = min( res, can_use ? min( solve( i, can_use - 1, p ) + _root[ now ][ i ] / 2, solve( i, can_use, p ) + _root[ now ][ i ] ) : solve( i, can_use, p ) + _root[ now ][ i ] );
	}
	return dp[ now ][ can_use ] = res;
}

int main() {
	while ( ~scanf("%d %d %d %d %d", &c, &n, &m, &s, &d) && n && m ) {
		--s;
		--d;
		for ( int i = 0; i < n; ++i ) {
			for ( int j = 0; j < n; j++ ) {
				_root[ i ][ j ] = 1 << 30;
			}
			_root[ i ][ i ] = 0;
		}
		for ( int i = 0; i < m; ++i ) {
			int a, b, f;
			scanf( "%d %d %d", &a, &b, &f );
			--a;
			--b;
			_root[ a ][ b ] = _root[ b ][ a ] = f;
		}
		NCLR( dp );
		int ans = solve( s, c, set<int>() );
		printf( "%d\n", ans );
	}
	return 0;
}

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

struct Data{
  int id;
  int cost;
  int ticket;
};
bool operator<(Data a, Data b){
  return a.cost!=b.cost?a.cost>b.cost:(a.ticket!=b.ticket?a.ticket<b.ticket:a.id>b.id);
}
struct Data2{
  int id;
  int ticket;
};
bool operator<(Data2 a, Data2 b){
  return a.id!=b.id?a.id>b.id:a.ticket<b.ticket;
}

#define NONE INT_MAX

int Dijkstra(vector< vector<int> >A,int start,int goal,int ticket)
{
  vector<int>cost(A.size(),NONE);
  priority_queue<Data>q;
  set<Data2>used;

  Data node={start,0,ticket};
  q.push(node);
  cost[start]=0;

  while(q.size()){
    node=q.top();q.pop();
    if(node.id==goal)return node.cost;
    Data2 t={node.id,node.ticket};
    if(used.count(t))continue;
    used.insert(t);
    for(int i=0;i<A[node.id].size();i++){
      if(A[node.id][i]==NONE)continue;
      if(cost[i]>cost[node.id]+A[node.id][i]){
	Data next={i,cost[node.id]+A[node.id][i],node.ticket};
	cost[i]=next.cost;
	q.push(next);
      }
      if(node.ticket){
	if(cost[i]>cost[node.id]+(A[node.id][i])/2){
	  Data next={i,cost[node.id]+(A[node.id][i])/2,node.ticket-1};
	  cost[i]=next.cost;
	  q.push(next);
	}
      }
    }
  }
  return -1;
}

int main()
{
  int c,n,m,s,d;
  int a,b,f;
  while(cin>>c>>n>>m>>s>>d,c|n|m|s|d){
    s--;d--;
    vector< vector<int> >A(n,vector<int>(n,NONE));
    for(int i=0;i<m;i++){
      cin>>a>>b>>f;
      a--;b--;
      A[a][b]=A[b][a]=f;
    }
    cout<<Dijkstra(A,s,d,c)<<endl;
  }
}

C++: #include<cstdio>
#include<iostream>
#include<vector>
#include<queue>
using namespace std;
#define INF 1e+8
class Data {
public:
	int to,cost,num;
	Data(){}
	Data(int to, int cost, int num):to(to),cost(cost),num(num){}
	bool operator<(const Data &s) const {
		if(cost != s.cost) return cost > s.cost;
		return to < s.to;
	}
};

int main() {
	int c,n,m,s,g;
	while(scanf("%d%d%d%d%d",&c,&n,&m,&s,&g),(c|n|m|s|g)) {
		vector<Data> G[128];
		for(int i = 0; i < m; i++) {
			int a,b,f;
			scanf("%d%d%d",&a,&b,&f);
			G[a].push_back(Data(b,f,0));
			G[b].push_back(Data(a,f,0));
		}
		bool memo[11][101] = {{}};
		priority_queue<Data> Q;
		Q.push(Data(s,0,c));
		int ans = -1;
		while(!Q.empty()) {
			Data e = Q.top();Q.pop();
			int v = e.to;
			if(memo[e.num][e.to]) continue;
			memo[e.num][e.to] = true;
			if(v == g) {
				ans = e.cost;
				break;
			}
			for(int i = 0; i < G[v].size(); i++) {
				Data E = G[v][i];
				if(e.num != 0) {
					Q.push(Data(E.to,E.cost/2 + e.cost,e.num-1));
				}
				Q.push(Data(E.to,E.cost + e.cost,e.num));
			}
		}
		printf("%d\n",ans);
	}
	return 0;
}