Go: package main

import (
	"container/heap"
	"fmt"
)

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
}

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)
		}
		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)
		start := Node{NowPosition: s, DiscountTicketTCount: c, Amount: 0}
		heap.Push(&pq, &start)
		for len(pq) != 0 {
			now := heap.Pop(&pq).(*Node)
			if now.NowPosition == d {
				fmt.Println(now.Amount)
				break
			}
			for _, v := range pointMap[now.NowPosition] {
				next := &Node{v.NextPoint, now.DiscountTicketTCount, now.Amount + v.Fee}
				heap.Push(&pq, next)
				if now.DiscountTicketTCount > 0 {
					next = &Node{v.NextPoint, now.DiscountTicketTCount - 1, now.Amount + v.Fee/2}
					heap.Push(&pq, next)
				}
			}
		}
	}
}

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

#define N 104
#define C 53
#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<algorithm>

const int MAX = (1<<30);

using namespace std;

int minnode;

int main(){
  int c, city, bus, from, to;
  while(cin >> c >> city >> bus >> from >> to && c && city && bus && from && to){

    int price[city+1][city+1];

    for(int i = 0; i < city+1; i++){
      for(int j = 0; j < city+1; j++){	
	price[i][j] = 0;	
      }
    }

    for(int i = 0; i < bus; i++){
      int start, end, pri;
      cin >> start >> end >> pri;

      price[start][end] = pri;
      price[end][start] = pri;
    }

    int node[city+1][c+1];
    int visited[city+1][c+1];

    for(int i = 0; i < city+1; i++){
      for(int j = 0; j < c+1; j++){	
	node[i][j] = MAX;
	visited[i][j] = 0;
      }
    }

    minnode = from;
    int ticket = c;
    node[from][c] = 0;
    int nownode = MAX;
    int minpos, mintic;
    
    while(1){
      for(int i = 1; i < city+1; i++){
	for(int j = 1; j < c+1; j++){
	  if(visited[i][j]) continue;
	  if(node[i][j] < nownode){
	    nownode = node[i][j];
	    minpos = i;
	    mintic = j;
	  }
	}
      }
      visited[minpos][mintic] = 1;
      if(nownode == MAX) break;
      
      nownode = MAX;
      
      for(int i = 1; i < city+1; i++){
	if(price[minpos][i]){
	  node[i][mintic] = min(node[i][mintic],node[minpos][mintic]+price[minpos][i]);
	  if(mintic){
	    node[i][mintic-1] = min(node[i][mintic-1],node[minpos][mintic] + price[minpos][i]/2);
	  }
	}
      }
    }

    for(int i = 1; i <= ticket; i++){
      if(node[to][0] > node[to][i]) node[to][0] = node[to][i];
    }
    cout << node[to][0] << endl;
  }
  return 0;
}

C++: // AOJ 0212 (http://judge.u-aizu.ac.jp/onlinejudge/description.jsp?id=0212)
#include <cstdio>
#include <algorithm>
#include <limits>
#include <queue>
#include <utility>
#include <vector>
#define repi(i,a,b) for(int i=(a);i<(b);++i)
#define rep(i,a) repi(i,0,a)

constexpr int MAX_N = 100, INF = std::numeric_limits<int>::max()>>2;

using P = std::pair<int, std::pair<int, int>>;

struct edge
{
  int to, cost;

  edge( int to, int cost )
  : to(to), cost(cost)
  {}
};

int c, n, m, s, d;
std::vector<edge> G[MAX_N];
int dp[MAX_N][11];

int main()
{
  while( scanf( "%d%d%d%d%d", &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;
      scanf( "%d%d%d", &a, &b, &f );
      --a; --b;
      G[a].emplace_back( edge( b, f ) );
      G[b].emplace_back( edge( a, f ) );
    }

    std::fill( (int*)dp, (int*)(dp+n), INF );

    std::priority_queue<P, std::vector<P>, std::greater<P>> pque;
    pque.push( P( 0, std::make_pair( s, 0 ) ) );
    dp[s][0] = 0;
    while( !pque.empty() )
    {
      P p = pque.top(); pque.pop();
      int dist = p.first, v = p.second.first, ticket = p.second.second;

      if( dist > dp[v][ticket] )
        continue;

      for( auto e : G[v] )
      {
        if( dp[e.to][ticket] > dist+e.cost )
        {
          dp[e.to][ticket] = dist+e.cost;
          pque.push( P( dp[e.to][ticket], std::make_pair( e.to, ticket ) ) );
        }
        if( ticket < 10 && dp[e.to][ticket+1] > dist+e.cost/2 )
        {
          dp[e.to][ticket+1] = dist+e.cost/2;
          pque.push( P( dp[e.to][ticket+1], std::make_pair( e.to, ticket+1 ) ) );
        }
      }
    }

    printf( "%d\n", *std::min_element( dp[d], dp[d]+c+1 ) );
  }

  return 0;
}