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 VVI _root;

uint solve( int now, int can_use, set<int> p ) {
	p.insert( now );
	if ( now == d ) {
		return 0;
	}
	if ( dp[ can_use ][ now ] != -1 ) {
		return dp[ can_use ][ now ];
	}
	uint 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[ now ][ can_use ] = res;
}

int main() {
	while ( ~scanf("%d %d %d %d %d", &c, &n, &m, &s, &d) && n && m ) {
		_root.resize( n, VI( n ) );
		--s;
		--d;
		for ( int i = 0; i < n; i++ ) {
			for ( int j = 0; j < n; j++ ) {
				_root[ i ][ j ] = INF;
				if ( i == j ) {
					_root[ i ][ j ] = 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 );
		uint ans = solve( s, c, set<int>() );
		printf( "%d\n", ans );
		_root.clear();
	}
	return 0;
}

C++: #include <cstdio>
#include <queue>
#include <vector>
#include <utility>
#include <algorithm>
using namespace std;
typedef pair<int,int> _P;
typedef pair<_P,int> P;
int main() {
	int c,n,m,s,d;
	int a,b,f;
	int i,ans;
	int cost1[100][100],cost2[100][11];
	priority_queue<P,vector<P>,greater<P> > que;
	while(scanf("%d%d%d%d%d",&c,&n,&m,&s,&d),c) {
		fill(cost1[0],cost1[0]+100*100,1<<30);
		fill(cost2[0],cost2[0]+100*11,1<<30);
		for(i=0;i<m;i++) {
			scanf("%d%d%d",&a,&b,&f);
			cost1[a-1][b-1]=cost1[b-1][a-1]=min(cost1[a-1][b-1],f);
		}
		que.push(P(_P(s-1,0),0));
		cost2[s-1][0]=0;
		while(!que.empty()) {
			P p=que.top();que.pop();
			if(cost2[p.first.first][p.second]<p.first.second) break;
			for(i=0;i<n;i++) {
				if(p.first.second+cost1[p.first.first][i]<cost2[i][p.second]) {
					cost2[i][p.second]=p.first.second+cost1[p.first.first][i];
					que.push(P(_P(i,cost2[i][p.second]),p.second));
				}
				if(p.second+1<=m&&(p.first.second+cost1[p.first.first][i]/2)<cost2[i][p.second+1]) {
					cost2[i][p.second+1]=p.first.second+cost1[p.first.first][i]/2;
					que.push(P(_P(i,cost2[i][p.second+1]),p.second+1));
				}
			}
		}
		ans=1<<30;
		for(i=0;i<=m;i++) if(ans>cost2[d-1][i]) ans=cost2[d-1][i];
		printf("%d\n",ans);
	}
}

C++: #include <iostream>
#include <vector>
#include <map>
#include <algorithm>
#define INF 1000010;

using namespace std;


int main(void){
  long c,n,m,s,d;
  while(true){
    cin>>c>>n>>m>>s>>d;
    if(c==0 and n==0 and m==0 and s==0 and d==0)break;
    d--;
    s--;

    long a,b,f;
    map<long,long> costs[n];
    for(int i=0;i<m;i++){
      cin>>a>>b>>f;
      a--;
      b--;
      costs[a][b]=f;
      costs[b][a]=f;
    }
    map<long,long> dist[n];
    for(long i=0;i<n;i++){
      for(long j=0;j<=c;j++){
        dist[i][j]=INF;
      }
    }
    dist[s][0]=0;

    vector<long> next,_next;
    next.push_back(s);
    while(next.empty()==false){
      _next.clear();
      for(auto iter=next.begin();iter!=next.end();iter++){
        long city=*iter;
        for(auto iter2=costs[city].begin();iter2!=costs[city].end();iter2++){
          long next_city=iter2->first;
          long fee=iter2->second;
          for(long ticket=0;ticket<=c;ticket++){
            if(dist[next_city][ticket]>dist[city][ticket]+fee){
              dist[next_city][ticket]=dist[city][ticket]+fee;
              _next.push_back(next_city);
            }
          }
          for(long ticket=1;ticket<=c;ticket++){
            if(dist[next_city][ticket]>dist[city][ticket-1]+fee/2){
              dist[next_city][ticket]=dist[city][ticket-1]+fee/2;
              _next.push_back(next_city);
            }
          }
        }
      }

      sort(_next.begin(),_next.end());
      _next.erase(unique(_next.begin(),_next.end()),_next.end());
      next.clear();
      copy(_next.begin(),_next.end(),back_inserter(next));

    }
    long retval=INF;
    for(long ticket=0;ticket<=c;ticket++){
        retval=min(dist[d][ticket],retval);
    }
    cout<<retval<<endl;
  }
}