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 <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 << 25;
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 uint _root[ 101 ][ 101 ];

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 ];
	}
	uint res = 1 << 30;
	for ( int i = 0; i < n; ++i ) {
		if ( p.count( i ) || _root[ now ][ i ] >= res ) {
			continue;
		}
		res = min( res, can_use ? min( solve( i, can_use - 1, p ) + _root[ now ][ i ] / 2, solve( i, can_use, p ) + _root[ now ][ i ] ) : solve( i, can_use, p ) + _root[ now ][ i ] );
	}
	return dp[ now ][ can_use ] = 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 ] = 1 << 30;
			}
			_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 <vector>
#include <queue>
using namespace std;

struct state {
  int node;
  int ticket;
  int cost;
  state(int n, int t, int c) : node(n), ticket(t), cost(c) {}
  bool operator<(const state& s) const
  {
    return cost > s.cost;
  }
};

int main()
{
  int c, n, m, s, d;
  while (cin >> c >> n >> m >> s >> d && c != 0) {
    --s;  --d;
    vector<vector<pair<int,int> > > g(n);
    for (int i = 0; i < m; i++) {
      int a, b, f;
      cin >> a >> b >> f;
      --a;  --b;
      g[a].push_back(make_pair(b, f));
      g[b].push_back(make_pair(a, f));
    }

    priority_queue<state> q;
    q.push(state(s, c, 0));
    vector<vector<int> > city(n, vector<int>(c, 1000000));
    city[s][c] = 0;
    while (!q.empty()) {
      const state s = q.top();
      q.pop();
      if (s.node == d) {
        cout << s.cost << endl;
        break;
      }

      city[s.node][s.ticket] = s.cost;
      for (vector<pair<int,int> >::const_iterator it(g[s.node].begin()); it != g[s.node].end(); ++it) {
        const int next = it->first;
        const int cost = s.cost + it->second;
        if (cost < city[next][s.ticket]) {
          city[next][s.ticket] = cost;
          q.push(state(next, s.ticket, cost));
        }
        if (s.ticket > 0) {
          const int cost2 = s.cost + it->second/2;
          if (cost2 < city[next][s.ticket-1]) {
            city[next][s.ticket-1] = cost2;
            q.push(state(next, s.ticket-1, cost2));
          }
        }
      }
    }
  }
  return 0;
}

C++: #include <iostream>
#include <cstdio>
#include <cstring>
#include <cstdlib>
#include <cmath>
#include <vector>
#include <string>
#include <map>
#include <set>
#include <queue>
#include <stack>
#include <algorithm>

using namespace std;

#define rep(i,j) REP((i), 0, (j))
#define REP(i,j,k) for(int i=(j);(i)<(k);++i)
#define BW(a,x,b) ((a)<=(x)&&(x)<=(b))
#define ALL(v) (v).begin(), (v).end()
#define LENGTHOF(x) (sizeof(x) / sizeof(*(x)))
#define AFILL(a, b) fill((int*)a, (int*)(a + LENGTHOF(a)), b)
#define MP make_pair
#define PB push_back
#define F first
#define S second
#define INF 1 << 30
#define EPS 1e-10

typedef pair<int, int> pi; // 残りの割引券 現在の街
typedef pair<int, pi>P; // コスト pi
typedef vector<int> vi;
typedef queue<int> qi;
typedef long long ll;

struct edge{ int to, cost; };

int C, V, E, S, D;
int d[128][16];
 vector<vector<edge> >G(128);
// int G[128];

void dijkstra(int s){
  priority_queue<P, vector<P>, greater<P> >q;
  rep(i, V) rep(j, C+1) d[i][j] = INF;
  d[s][C] = 0;
  q.push(MP(0, MP(C, s)));

  while(!q.empty()){
    P p = q.top(); q.pop();
    int v = p.S.S;
    int c = p.S.F;

    rep(i, G[v].size()){
      edge e = G[v][i];
      if(d[e.to][c] > d[v][c] + e.cost){
	d[e.to][c] = d[v][c] + e.cost;
	q.push(MP(d[e.to][c], MP(c, e.to)));
      }

      if( c > 0 && d[e.to][c-1] > d[v][c] + e.cost/2){
	  d[e.to][c-1] = d[v][c] + e.cost/2;
	  q.push(MP(d[e.to][c-1], MP(c-1, e.to)));
      }
    }
  }
}

int main(){
  while(scanf("%d%d%d%d%d", &C, &V, &E, &S, &D) && C+V+E+S+D){
    S--; D--;
    rep(i, 128){
      //      rep(j, 128) G[i][j] = INF;
      G[i].clear();
    }
    rep(i, E){
      int a, b, c;
      scanf("%d%d%d", &a, &b, &c); a--; b--;
     edge e;
      e.to = a; e.cost = c;
      G[b].PB(e);
      e.to = b;
      G[a].PB(e);
      //      G[a][b] = G[b][a] = c;
    }

    dijkstra(S);

    int res = INF;
    rep(i, C+1) res = min(res, d[D][i]);
    printf("%d\n", res);
    //    printf("%d\n", d[D][0]);
  }

  return 0;
}