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;

typedef vector<int> vi;
typedef pair<int,int> pii;
typedef long long ll;

#define rep(i,n) for(ll i=0;i<(ll)(n);i++)
#define all(a)  (a).begin(),(a).end()
#define pb push_back
#define INF 999999999

int c,n,m;
int pass[200][200];

double d[200][20];
bool used[200][20];

int dijk(int s,int g){
    rep(i,200)rep(j,20){
        d[i][j]=INF;
        used[i][j]=false;
    }
    
    d[s][c]=0;
    
    while(1){
        int v=-1;
        int w=-1;
        rep(u,n){
            rep(i,c+1){
                if( !used[u][i] && (v==-1||d[u][i]<d[v][w]) )v=u,w=i;
            }
        }
        if(v==-1)break;
        
        used[v][w]=true;
        
        rep(u,n){
            d[u][w] = min(d[u][w] , d[v][w] + pass[v][u] );
//            cout<<"d["<<u<<"]["<<w<<"]="<<d[u][w]<<endl;
            if(w-1>=0 && pass[v][u]!=INF){
                d[u][w-1] = min(d[u][w-1] , d[v][w] + (pass[v][u]/2.0) );
//                cout<<"d["<<u<<"]["<<w-1<<"]="<<d[u][w-1]<<endl;
            }
        }
    }
    double ret=INF;
    rep(i,c+1){
        ret = min(ret,d[g][i]);
    }
    return ret;
}


int main(){
    int s,g;
    while(cin>>c>>n>>m>>s>>g){
        if(c==0&&n==0&&m==0&&s==0&&g==0)break;
        
        s--,g--;
        rep(i,200)rep(j,200)pass[i][j]=INF;
        rep(i,200)pass[i][i]=0;
        
        rep(i,m){
            int a,b,f;
            cin>>a>>b>>f;
            a--,b--;
            pass[a][b]=pass[b][a]=f;
        }
        
    cout<<dijk(s,g)<<endl;
    }
}

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

#define loop(i, n) for (int i = 0; i < n; i++)
#define INF 1010001000

typedef pair<int, int> i_i;
typedef struct data{int pos, tick, cost;}data;

int dp(vector<vector<i_i > > &g);

int c, n, m, s, d;

int main(void)
{
    while (cin >> c >> n >> m >> s >> d, c) {
        n++;
        vector<vector<i_i > > g(n);
        loop(i, m) {
            int a, b, f;
            cin >> a >> b >> f;
            g[a].push_back(i_i(f, b));
            g[b].push_back(i_i(f, a));
        }
        cout << dp(g) << endl;
    }
    return 0;
}

int dp(vector<vector<i_i > > &g)
{
    vector<vector<int> > table(c+1, vector<int>(n, INF));
    queue<data> a;
    data dt = {s, c, 0};
    a.push(dt);
    while (!a.empty()) {
        data tmp = a.front(); a.pop();
        for (i_i i : g[tmp.pos]) {
            if (table[tmp.tick][i.second] > tmp.cost + i.first) {
                table[tmp.tick][i.second] = tmp.cost + i.first;
                dt.pos = i.second; dt.tick = tmp.tick; 
                dt.cost = tmp.cost + i.first;
                a.push(dt);
            }
            if (tmp.tick && 
                    table[tmp.tick-1][i.second] > tmp.cost + i.first) {
                table[tmp.tick-1][i.second] = tmp.cost + i.first / 2;
                dt.pos = i.second; dt.tick = tmp.tick-1; 
                dt.cost = tmp.cost + i.first / 2;
                a.push(dt);
            }
        }
    }
    int ret = INF;
    for (int i = 0; i < c+1; i++) {
        ret = min(ret, table[i][d]);
    }
    return ret;
}

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

using namespace std;

#define INF 100000000

struct edge {
	int to, cost;
};

int main() {
	int c, n, m, s, d;
	while (cin >> c >> n >> m >> s >> d) {
		if (c == 0 && n == 0 && m == 0 && s == 0 && d == 0) {
			break;
		}
		vector<edge> ff[101];
		vector< vector<int> > ddd(n+1, vector<int>(n+1, INF));
		int a, b, f;
		for (int i = 0; i < m; i++) {
			cin >> a >> b >> f;
			edge e;
			e.to = b;
			e.cost = f;
			ff[a].push_back(e);
			e.to = a;
			ff[b].push_back(e);
			ddd[a][b] = ddd[b][a] = f;
		}
		for (int i = 1; i <= n; i++) {
			ddd[i][i] = 0;
		}
		for (int k = 1; k <= n; k++) {
			for (int i = 1; i <= n; i++) {
				for (int j = 1; j <= n; j++) {
					ddd[i][j] = min(ddd[i][j], ddd[i][k]+ddd[k][j]);
				}
			}
		}
		vector<int> isd[101];
		for (int i = 1; i <= n; i++) {
			for (int j = 1; j <= n; j++) {
				if (ddd[i][j] != INF) {
					isd[i].push_back(j);
				}
			}
		}
		vector< vector< vector<int> > > dp(n+1, vector< vector<int> >(n+1, vector<int>(c+1, INF)));
		for (int i = 1; i <= n; i++) {
			dp[s][i][0] = ddd[s][i];
		}
		for (int k = 1; k <= c; k++) {
			for (int p = 0; p < isd[s].size(); p++) {
				int pp = isd[s][p];
				dp[s][pp][k] = dp[s][pp][k-1];
				for (int i = 0; i < isd[s].size(); i++) {
					int ii = isd[s][i];
					for (int j = 0; j < isd[ii].size(); j++) {
						int jj = isd[ii][j];
						for (int q = 0; q < ff[jj].size(); q++) {
							int qq = ff[jj][q].to;
							if (ddd[qq][pp] == INF) continue;
							if (dp[s][pp][k] > dp[s][ii][k-1]+ddd[ii][jj]+(ff[jj][q].cost/2)+ddd[qq][pp]) {
								dp[s][pp][k] = dp[s][ii][k-1]+ddd[ii][jj]+(ff[jj][q].cost/2)+ddd[qq][pp];
							}
						}
					}
				}
			}
		}
		cout << dp[s][d][c] << endl;
	}
	return 0;
}