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 << 30;
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[ 100 ][ 1000 ];
static int _root[ 1000 ][ 1000 ];

int solve( int now, int can_use, set<int> p ) {
	if ( now == d ) {
		return 0;
	}
	p.insert( now );
	if ( dp[ can_use ][ now ] >= 0 ) {
		return dp[ can_use ][ now ];
	}
	int res = INF;
	for ( int i = 0; i < n; ++i ) {
		if ( p.count( i ) || _root[ now ][ i ] >= res ) {
			continue;
		}
		res = min( res, solve( i, can_use, p ) + _root[ now ][ i ] );
		if ( can_use ) {
			res = min<int>( res, solve( i, can_use - 1, p ) + _root[ now ][ i ] * 0.5 );
		}

	}
	return dp[ can_use ][ now ] = 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 ] = INF;
			}
			_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 ] = min( _root[ a ][ b ], f );
		}
		NCLR( dp );
		int ans = solve( s, c, set<int>() );
		printf( "%d\n", ans );
	}
	return 0;
}

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

#define INF 100000000

struct edge {
	int to;
	int f;
	edge(int to_, int f_) {
		to = to_; f = f_;
	}
	edge(){}
};
struct status {
	int vertex;
	int cost;
	int c;
	status(int vertex_, int cost_, int c_) {
		vertex = vertex_; cost = cost_; c = c_;
	}
	status(){}
	bool operator<(const status & obj) const {
		if(this->c != obj.c)
			return this->c < obj.c;
		return this->cost > obj.cost;
	}
};

int main() {
	while(true) {
		int c, n, m, s, d;
		cin >> c >> n >> m >> s >> d;
		if(!(c || n || m || s || d))
			break;
		s--; d--;
		vector<vector<edge> > v(n);
		for(int i = 0; i < m; i++) {
			int a, b, f;
			cin >> a >> b >> f;
			a--; b--;
			v[a].push_back(edge(b,f));
			v[b].push_back(edge(a,f));
		}
		priority_queue<status> q;
		int cost[128][16];
		for(int i = 0; i < 128; i++)
			for(int j = 0; j < 16; j++)
				cost[i][j] = INF;
		q.push(status(s, 0, c));
		while(!q.empty()) {
			status cur;
			cur = q.top(); q.pop();

			if(cost[cur.vertex][cur.c] == INF) {
				cost[cur.vertex][cur.c] = cur.cost;
				for(int i = 0; i < v[cur.vertex].size(); i++) {
					if(cost[v[cur.vertex][i].to][cur.c] == INF) {
						q.push(status(v[cur.vertex][i].to, v[cur.vertex][i].f + cur.cost, cur.c));
					}
					if(cur.c > 0 && cost[v[cur.vertex][i].to][cur.c-1] == INF) {
						q.push(status(v[cur.vertex][i].to, v[cur.vertex][i].f / 2 + cur.cost, cur.c - 1));
					}
				}
			}
		}

		int ret = INF;
		for(int i = 0; i <= c; i++) {
			ret = min(ret, cost[d][i]);
		}
		cout << ret << endl;
	}
}