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>
#include <vector>
#include <queue>
using namespace std;

struct State {
    int no_;
    int cost_;
    int ticket_;
    State(int no, int cost, int ticket) 
        : no_(no), cost_(cost), ticket_(ticket) {} 
    
};

struct Edge {
    int to_;
    int cost_;
    Edge(int to, int cost) 
        : to_(to), cost_(cost) {}
};

int c, n, m, s, d;

auto dijkstra(vector<vector<Edge>> &g, vector<vector<int>> &dm) -> int {
    auto comp = [](auto& lhs, auto& rhs){return lhs.cost_ > rhs.cost_;};
    priority_queue<State, vector<State>, decltype(comp)> que(comp);

    que.push(State(s, 0, c));
    for (auto &e : dm[s]) {
        e = 0;
    }
    while (!que.empty()) {
        State s = que.top();
        que.pop();
        int current_no = s.no_;
        int current_cost = s.cost_;
        int current_ticket = s.ticket_;
        for (auto &e : g[current_no]) {
            int to = e.to_;
            int cost = e.cost_;
            if (current_ticket > 0) {
                // not use ticket
                if (dm[to][current_ticket] > dm[current_no][current_ticket] + cost) {
                    que.push(State(to, dm[current_no][current_ticket] + cost, current_ticket));
                    dm[to][current_ticket] = dm[current_no][current_ticket] + cost;
                }
                // use ticket
                if (dm[to][current_ticket-1] > dm[current_no][current_ticket] + cost/2) {
                    que.push(State(to, dm[current_no][current_ticket] + cost/2, current_ticket-1));
                    dm[to][current_ticket-1] = dm[current_no][current_ticket-1] + cost/2;
                }
            }else {
                if (dm[to][current_ticket] > dm[current_no][current_ticket] + cost) {
                    que.push(State(to, dm[current_no][current_ticket] + cost, current_ticket));
                    dm[to][current_ticket] = dm[current_no][current_ticket] + cost;
                }
            }
        }
    }

    int ans = 1e8;
    for (auto &e : dm[d]) {
        ans = min(ans, e);
    }
    return ans;
}

auto main(int argc, char const *argv[]) -> int {
    constexpr int INF = 1e8;

    while(cin>>c>>n>>m>>s>>d, c||n||m||s||d) {
        vector<vector<Edge>> g(n+1);
        vector<vector<int>> dm(n+1);
        for (auto &e : dm) {
            for (int i = 0; i < c + 1; ++i) {
                e.push_back(INF);
            }
        }

        for (int i = 0; i < m; ++i) {
            int a, b, f;
            cin>>a>>b>>f;
            g[a].push_back(Edge(b, f));
            g[b].push_back(Edge(a, f));
        }

        for (int i = 0; i <= n; ++i) {
            for (auto &e : g[i]) {
                cout<<i<<" -> "<<e.to_<<" : "<<e.cost_<<endl;
            }
        }
        cout<<dijkstra(g, dm)<<endl;
    }
    return 0;
}

C++: #include <iostream>
#include <cstring>
#include <queue>
#include <utility>
#define rep2(x,from,to) for(int x=(from);(x)<(to);(x)++)
#define rep(x,to) rep2(x,0,to)
using namespace std;
const int INF = 1<<25;
int main(){
	int c, n, m, s, d, a, b, f;
	
	while(cin >> c >> n >> m >> s >> d && (c || m || n || s || d)) {
		s--, d--;
		int cost[110][110] = {}, ret[11][110];
		rep(i,m) {
			cin >> a >> b >> f;
			a--, b--;
			cost[a][b] = cost[b][a] = f;
		}
		rep(i,c+1) {
			rep(j,n) { 
				ret[i][j] = INF;
			}
		}
		queue<pair<int, int> > q;
		q.push(make_pair(c,s));
		ret[c][s] = 0;
		while(!q.empty()) {
			int node = q.front().second, nc = q.front().first; q.pop();
			rep(i,n) {
				if(cost[node][i]) {
					if(ret[nc][i] > ret[nc][node] + cost[node][i]) {
						ret[nc][i] = ret[nc][node] + cost[node][i];
						q.push(make_pair(nc, i));
					}
					if(nc>0 && ret[nc - 1][i] > ret[nc][node] + cost[node][i] / 2) {
						 ret[nc - 1][i] = ret[nc][node] + cost[node][i] / 2;
						 q.push(make_pair(nc-1, i));
					}
				}
			}	
		}
		int res = INF;
		rep(i,c+1) {
			res = min(res,ret[i][d]);
		}
		cout << res << endl;
	}
}