#include <bits/stdc++.h>
using namespace std;

typedef long long   signed int LL;
typedef long long unsigned int LU;

#define incID(i, l, r) for(int i = (l)    ; i <  (r); i++)
#define incII(i, l, r) for(int i = (l)    ; i <= (r); i++)
#define decID(i, l, r) for(int i = (r) - 1; i >= (l); i--)
#define decII(i, l, r) for(int i = (r)    ; i >= (l); i--)
#define  inc(i, n) incID(i, 0, n)
#define inc1(i, n) incII(i, 1, n)
#define  dec(i, n) decID(i, 0, n)
#define dec1(i, n) decII(i, 1, n)

#define inII(v, l, r) ((l) <= (v) && (v) <= (r))
#define inID(v, l, r) ((l) <= (v) && (v) <  (r))

#define PB push_back
#define EB emplace_back
#define MP make_pair
#define FI first
#define SE second
#define UB upper_bound
#define LB lower_bound
#define PQ priority_queue

#define  ALL(v)  v.begin(),  v.end()
#define RALL(v) v.rbegin(), v.rend()
#define  FOR(it, v) for(auto it =  v.begin(); it !=  v.end(); ++it)
#define RFOR(it, v) for(auto it = v.rbegin(); it != v.rend(); ++it)

template<typename T> bool   setmin(T & a, T b) { if(b <  a) { a = b; return true; } else { return false; } }
template<typename T> bool   setmax(T & a, T b) { if(b >  a) { a = b; return true; } else { return false; } }
template<typename T> bool setmineq(T & a, T b) { if(b <= a) { a = b; return true; } else { return false; } }
template<typename T> bool setmaxeq(T & a, T b) { if(b >= a) { a = b; return true; } else { return false; } }
template<typename T> T gcd(T a, T b) { return (b == 0 ? a : gcd(b, a % b)); }
template<typename T> T lcm(T a, T b) { return a / gcd(a, b) * b; }

// ---- ----

int n, m, k, a[1000], b[1000], c[1000], d[1000];
bool e[1001][1000];

int main() {
	cin >> n >> m >> k;
	inc(i, m) { cin >> a[i] >> b[i] >> c[i]; a[i]--; b[i]--; }
	inc(i, k) { cin >> d[i]; }
	
	inc(i, n) { e[0][i] = true; }
	
	inc(i, k) {
		inc(j, m) {
			if(e[i][ a[j] ] && c[j] == d[i]) { e[i + 1][ b[j] ] = true; }
			if(e[i][ b[j] ] && c[j] == d[i]) { e[i + 1][ a[j] ] = true; }
		}
	}
	
	int ans = 0;
	inc(i, n) { if(e[k][i]) { ans++; } }
	cout << ans << endl;
	
	bool flag = true;
	inc(i, n) {
		if(e[k][i]) {
			cout << (flag ? "" : " ") << (i + 1);
			flag = false;
		}
	}
	cout << endl;
	
	return 0;
}