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 <iostream>

#define MX 1000000000

using namespace std;
int cost[100][100],n;

int dijkstra(int s , int g , int c){
  bool visited[100];
  int d[100][11];
  for(int i=0;i <= c;i++){
    for(int j=0;j < n;j++) d[j][i] = MX , visited[j] = false;
    d[s][i] = 0;
      while(1){
        int u;
        int mincost = MX;
        for(int j=0;j<n;j++)if(!visited[j] && d[j][i] < mincost) mincost = d[j][i],u = j;
        if(mincost == MX) break;
        visited[u] = true;
        for(int v = 0;v < n;v++){
          if(visited[v] || cost[u][v] == MX) continue;
          if(d[v][i] > d[u][i] + cost[u][v]) d[v][i] = d[u][i] + cost[u][v];
          if(i > 0) if(d[v][i] > d[u][i-1] + cost[u][v] / 2) d[v][i] = d[u][i-1] + cost[u][v] / 2;
        }
      }
  }
  return d[g][c];
}

int main(){
  int c,m,s,d;
  while(cin >> c >> n >> m >> s >> d && (c|n|m|s|d)){
    for(int i=0;i<n;i++)for(int j=0;j<n;j++) cost[i][j] = MX;
    while(m--){
      int a,b;
      cin >> a >> b;
      cin >> cost[a-1][b-1];
      cost[b-1][a-1] = cost[a-1][b-1];
    }
    cout << dijkstra(s-1,d-1,c) << endl;
  }
  return 0;
}

C++: #include <bits/stdc++.h>
#define PB push_back
#define MP make_pair
#define REP(i,n) for (int i=0;i<(n);i++)
#define FOR(i,a,b) for(int i=(a);i<(b);i++)
#define ALL(a) (a).begin(),(a).end()
using namespace std;
typedef long long ll;
typedef unsigned long long ull;
typedef pair<int,int> P;
double EPS=1e-10;
int INF=1e9;
static const int MEM_SIZE=1000000;
struct edge{int to,cost;};
struct dat{
      int s,cost,num;
      dat(int s,int cost,int num):s(s),cost(cost),num(num){}
      bool operator<(const dat& a)const{return cost<a.cost;}
};
vector<edge> G[100];
int dist[100][11];
int n,c;
void dijkstra(int s){
      REP(i,100)REP(j,11)dist[i][j]=INF;
      priority_queue<dat>Q;
      Q.push(dat(s,0,0));
      dist[s][0]=0;
      while(!Q.empty()){
            dat p=Q.top();Q.pop();
            if(p.cost>dist[p.s][p.num])continue;
            REP(i,G[p.s].size()){
                  edge e=G[p.s][i];
                  if(p.num<c){
                        if(dist[p.s][p.num]+e.cost/2<dist[e.to][p.num+1]){
                              dist[e.to][p.num+1]=dist[p.s][p.num]+e.cost/2;
                              Q.push(dat(e.to,dist[e.to][p.num+1],p.num+1));
                        }
                  }else{
                        if(dist[p.s][p.num]+e.cost<dist[e.to][p.num]){
                              dist[e.to][p.num]=dist[p.s][p.num]+e.cost;
                              Q.push(dat(e.to,dist[e.to][p.num],p.num));
                        }
                  }
            }
      }
}
int main(){
      int m,s,d;
      while(cin>>c>>n>>m>>s>>d&&(c||n||m||s||d)){
            s--;d--;
            REP(i,100)G[i].clear();
            REP(i,m){
                  int a,b,f;
                  cin>>a>>b>>f;
                  a--;b--;
                  G[a].PB((edge){b,f});
                  G[b].PB((edge){a,f});
            }
            dijkstra(s);
            int ans=INF;
            /*REP(i,n){
                  REP(j,c+1){
                        cout<<dist[i][j];
                        if(j==c-1)cout<<endl;
                        else cout<<" ";
                        //cout<<i<<" "<<j<<endl;
                  }
            }*/
            REP(i,c+1)ans=min(ans,dist[d][i]);
            cout<<ans<<endl;
      }
}

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

using namespace std;

struct P {
	int from, cost, coupon;

	bool operator >(const P& p) const {
		return cost > p.cost;
	}
};

int ecost[101][101];
int ccost[101][11];
int c, n, m, s, d;
int i;

int main() {
	while(cin >> c >> n >> m >> s >> d, c|n|m|s|d) {
		fill_n((int *)ecost, 101*101, -1);
		fill_n((int *)ccost, 101*11, 1e8);
		for(i=0; i<11; i++) ccost[s][i] = 0;
		for(i=0; i<m; i++){
			int a, b, f;
			cin >> a >> b >> f;
			ecost[a][b] = f;
			ecost[b][a] = f;
		}
		priority_queue<P, vector<P>, greater<P>> q;
		q.push((P){s, 0, 0});
		int dcost;
		while(!q.empty()){
			P p = q.top(); q.pop();
			// cout << "pos=" << p.from << endl;
			// goal
			if(p.from == d) {
				dcost = p.cost;
				break;
			}
			//
			for(i=0; i<n+1; i++){ // i:to
				if(ecost[p.from][i] != -1){
					bool ifpush = true;
					for(int j=0; j <= p.coupon; j++) ifpush = ifpush && p.cost + ecost[p.from][i] < ccost[i][j];
					if(ifpush) {
					//if(p.cost + ecost[p.from][i] < ccost[i][p.coupon]){
						q.push((P){i, p.cost + ecost[p.from][i], p.coupon});
					}
					if(p.coupon+1 <= c) {
						bool ifpush = true;
						for(int j=0; j <= p.coupon+1; j++) ifpush = ifpush && p.cost + ecost[p.from][i]/2 < ccost[i][j];
						if(ifpush) {
						// if(p.cost + ecost[p.from][i]/2 < ccost[i][p.coupon+1]){
							q.push((P){i, p.cost + ecost[p.from][i]/2, p.coupon+1});
						}
					}
				}
			}
		}
		cout << dcost << endl;
	}
	return 0;
}