Go: package main

import (
	"container/heap"
	"fmt"
	"runtime"
)

type Node struct {
	NowPosition          int
	DiscountTicketTCount int
	Amount               int
}

type PriorityQueueNode []*Node

func (pq PriorityQueueNode) Len() int {
	return len(pq)
}

func (pq PriorityQueueNode) Less(i, j int) bool {
	return pq[i].Amount < pq[j].Amount
}

func (pq PriorityQueueNode) Swap(i, j int) {
	pq[i], pq[j] = pq[j], pq[i]
}

func (pq *PriorityQueueNode) Push(node interface{}) {
	*pq = append(*pq, node.(*Node))
}

func (pq *PriorityQueueNode) Pop() interface{} {
	old := *pq
	n := len(old)
	item := old[n-1]
	*pq = old[0 : n-1]
	return item
}

type Point struct {
	NextPoint int
	Fee       int
}

type Memo struct {
	NowPoint             int
	DiscountTicketTCount int
}

func main() {
	var c, n, m, s, d int
	var a, b, f int

	for {
		fmt.Scan(&c, &n, &m, &s, &d)
		if c == 0 && n == 0 && m == 0 && s == 0 && d == 0 {
			break
		}
		s--
		d--
		pointMap := make([][]Point, n)
		for i := 0; i < n; i++ {
			pointMap[i] = make([]Point, 0, n)
		}
		for i := 0; i < m; i++ {
			fmt.Scan(&a, &b, &f)
			a--
			b--
			pointMap[a] = append(pointMap[a], Point{NextPoint: b, Fee: f})
			pointMap[b] = append(pointMap[b], Point{NextPoint: a, Fee: f})
		}
		pq := make(PriorityQueueNode, 0, m)
		start := Node{NowPosition: s, DiscountTicketTCount: c, Amount: 0}
		heap.Push(&pq, &start)
		memo := make(map[Memo]struct{})
		for len(pq) != 0 {
			now := heap.Pop(&pq).(*Node)
			if now.NowPosition == d {
				fmt.Println(now.Amount)
				break
			}
			memo[Memo{NowPoint: now.NowPosition, DiscountTicketTCount: now.DiscountTicketTCount}] = struct{}{}
			for _, v := range pointMap[now.NowPosition] {
				next := &Node{v.NextPoint, now.DiscountTicketTCount, now.Amount + v.Fee}
				if _, ok := memo[Memo{NowPoint: v.NextPoint, DiscountTicketTCount: now.DiscountTicketTCount}]; !ok {
					heap.Push(&pq, next)
				}
				if now.DiscountTicketTCount > 0 {
					next = &Node{v.NextPoint, now.DiscountTicketTCount - 1, now.Amount + v.Fee/2}
					if _, ok := memo[Memo{NowPoint: v.NextPoint, DiscountTicketTCount: now.DiscountTicketTCount}]; !ok {
						heap.Push(&pq, next)
					}
				}
			}
		}
		runtime.GC()
	}
}

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 << 30;
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;
LL dp[ 11 ][ 101 ];
static LL _root[ 100 ][ 100 ];

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

	}
	return dp[ can_use ][ now ] = 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 ] = LL_INF;
			}
			_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 );
		LL ans = solve( s, c, set<int>() );
		printf( "%lld\n", ans );
	}
	return 0;
}

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

#define INF ((int)1e9)

struct Edge {
  int to, cost;
  Edge(int t, int c) : to(t), cost(c) {}
};

typedef pair<int, int> Pii;
typedef pair<int, Pii> Piii; // cost, node, cnum

vector<Edge> G[100];
int memo[100][10];

int dijkstra(int src, int dst, int cnum) {
  
  fill(memo[0], memo[0]+1000, INF);
  
  priority_queue<Piii> pq;
  memo[src][cnum] = 0;
  pq.push(Piii(0, Pii(src, -cnum)));
  while(!pq.empty()) {
    const Piii get = pq.top(); pq.pop();
    int cost = get.first;
    int cn = -get.second.second;
    int now = get.second.first;
    
    for(int i=0; i<G[now].size(); i++) {
      int next = G[now][i].to;
      int add_c = G[now][i].cost;
      if(memo[next][cn] > cost + add_c) {
	pq.push(Piii(cost+add_c, Pii(next, -cn)));
	memo[next][cn] = cost + add_c;
      }
      if(cn-1<0) continue;
      add_c /= 2;
      if(memo[next][cn-1] > cost + add_c) {
	pq.push(Piii(cost+add_c, Pii(next, 1-cn)));
	memo[next][cn-1] = cost + add_c;
      }
    }
  }
  
  return *min_element(memo[dst], memo[dst]+10);
}

int main() {
  int C, N, M, S, D;
  while(cin >> C >> N >> M >> S >> D && (N|M)) {
    for(int i=0; i<N; i++) {
      G[i].clear();
    }
    for(int i=0; i<M; i++) {
      int a, b, c; cin >> a >> b >> c; a--, b--;
      G[a].push_back(Edge(b, c));
      G[b].push_back(Edge(a, c));
    }
    
    S --, D --;
    cout << dijkstra(S, D, C) << endl;
  }
  
  return 0;
}

C++: #include <cstdio>
#include <vector>
#include <algorithm>
#include <functional>
#include <queue>
using namespace std;

struct state{
	int pos;
	int ticket;
	int sum;
	
	bool operator< (const state &s) const{
		return s.sum < sum;
	}
};

struct edge{
	int to;
	int fee;
};

int c, n, m, s, d;
vector<vector<edge> > G;

int solve(){
	vector<vector<int> > v(n + 1, vector<int>(c + 1, 1000000000));

	priority_queue<state> pq;
	pq.push((state){s, c, 0});
	v[s][c] = 0;

	while(!pq.empty()){
		state st = pq.top();
		pq.pop();

		if(v[st.pos][st.ticket] != st.sum){ continue; }
		if(st.pos == d) return st.sum;

		for(int i = 0; i < G[st.pos].size(); ++i){
			int t = G[st.pos][i].to;
			int f = G[st.pos][i].fee + st.sum;
			if(v[t][st.ticket] > f){
				v[t][st.ticket] = f;
				pq.push((state){t, st.ticket, f});
			}
			
			if(st.ticket > 0){
				f = G[st.pos][i].fee / 2 + st.sum;
				if(v[t][st.ticket - 1] > f){
					v[t][st.ticket - 1] = f;
					pq.push((state){t, st.ticket - 1, f});
				}
			}
		}
	}
	return -1;
}

int main(){
	int a, b, f;
	while(scanf("%d%d%d%d%d", &c, &n, &m, &s, &d), n){
		G.assign(n + 1, vector<edge>());
		for(int i = 0; i < m; ++i){
			scanf("%d%d%d", &a, &b, &f);
			G[a].push_back((edge){b, f});
			G[b].push_back((edge){a, f});
		}
		
		printf("%d\n", solve());
	}
}