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 <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;
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 ] == INF ) {
			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 ] = 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 );
		int ans = solve( s, c, set<int>() );
		printf( "%d\n", ans );
	}
	return 0;
}

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

using namespace std;

const int INF = 10000000;

int solve( int city[101][101], int s, int d, int c, int n ){
	int dist[11][101];
	int history[101];

	for( int i = 0;i < 11;i++ ){
		for( int j = 0;j < 101;j++ ){
			dist[i][j] = INF;
		}
	}

	for( int i = 0;i < 101;i++ ){
		history[i] = 0;
	}

	for( int i = 0;i < 11;i++ ) dist[i][s] = 0;

	typedef pair<int,int> data;
	typedef pair<int,data> graph;
	priority_queue<graph,vector<graph>,greater<graph> > q;

	q.push( graph( 0, data( s, c ) ) );

	while( !q.empty() ){
		graph a = q.top();
		int u = a.second.first;
		int uc = a.second.second;
		q.pop();
		history[u] = 1;

		for( int i = 1;i <= n;i++ ){
			if( city[u][i] == INF || history[i] ) continue;

			if( dist[uc][i] > dist[uc][u] + city[u][i] ){
				dist[uc][i] = dist[uc][u] + city[u][i];
				q.push( graph( dist[uc][i], data( i, uc ) ) );
			}

			if( uc && dist[uc - 1][i] > dist[uc][i] + city[u][i] / 2 ){
				dist[uc - 1][i] = dist[uc][u] + city[u][i] / 2;
				q.push( graph( dist[uc - 1][i], data( i, uc - 1 ) ) );
			}
		}
	}
	return dist[0][d];

}

int main(int argc, char const* argv[])
{
	int c,n,m,s,d;
	int city[101][101];

	while( cin >> c >> n >> m >> s >> d && c != 0 ){
		int a,b,f;
		for( int i = 0;i < 101;i++ ){
			for( int j = 0;j < 101;j++ ){
				city[i][j] = INF;
			}
		}
		for( int i = 0;i < m;i++ ){
			cin >> a >> b >> f;
			city[a][b] = f;
			city[b][a] = f;
		}

		cout << solve( city, s, d, c, n ) << endl;
	}

	return 0;
}

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

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

const int INF = 1 << 21;
const int MAX_C = 10, MAX_N = 100, MAX_M = 500;

int dp[MAX_N + 1][MAX_C + 1], w[MAX_N + 1][MAX_N + 1];
int c, n, m, s, d;

int solve()
{
    for(int i = 0; i <= MAX_N; i++) 
        for(int j = 0; j <= MAX_C; j++) 
            dp[i][j] = INF;
    
    priority_queue<P, vector<P>, greater<P> > que;
    que.push(P(0, S(s, c)));
    while(!que.empty()) {
        P p = que.top(); que.pop();
        int cost = p.first,  from = p.second.first, t = p.second.second;
        
        if(from == d)
            return cost;

        for(int to = 1; to <= n; to++) {
            if(cost + w[from][to] < dp[to][t]) {
                dp[to][t] = cost + w[from][to];
                que.push(P(dp[to][t], S(to, t)));
            }
        }

        if(t > 0) {
            for(int to = 1; to <= n; to++) {
                if(w[from][to] / 2 + cost < dp[to][t - 1]) {
                    dp[to][t - 1] = w[from][to] / 2 + cost;
                    que.push(P(dp[to][t-1], S(to, t - 1)));
                }
            }
        }
    }
}

int main()
{
    while(cin >> c >> n >> m >> s >> d && c || n || m) {

        for(int i = 0; i <= n; i++) 
            for(int j = 0; j <= n; j++)
                w[i][j] = INF;
        int a, b, f;
        for(int k = 0; k < m; k++) {
            cin >> a >> b >> f;
            w[a][b] = w[b][a] = f;
        }

        cout << solve() << endl;
    }
}