#define _USE_MATH_DEFINES
#pragma GCC target("avx2")
#pragma GCC optimize("O3")
#pragma GCC optimize("unroll-loops")

#include<bits/stdc++.h>
//#include<unordered_set>
//#include<random>
//#include <array>
//#include <complex>
//#include<chrono>
//#include<boost/multiprecision/cpp_int.hpp>
//#include <atcoder/all>
//using namespace boost::multiprecision;

using namespace std;
//using namespace atcoder;
#define LP(I,S,G) for (long long int I = (S); I < (G); ++I)
#define IN(X) 	for (int in = 0; in < X.size(); in++)cin >> X[in]
#define OUT(X) 	for (int in = 0; in < X.size(); in++)cout << X[in]<<" "
#define SORT(X) sort((X).begin(), (X).end())
#define CSORT(X,Y) sort(X.begin(), X.end(),Y)
#define COPY(X,Y) copy(X.begin(), X.end(), Y.begin())
#define ALL(X,Y) for (auto &(X) :(Y))
#define FULL(a)  (a).begin(),(a).end()
#define BFS(Q,S) for(Q.push(S);Q.size()!=0;Q.pop())
typedef long long int ll;
typedef unsigned long long int ull;
long long int M = 998244353;

chrono::system_clock::time_point starttime;
using namespace std::chrono;

inline float getTime() {
	return duration_cast<milliseconds>(system_clock::now() - starttime).count();
}


int dx[] = { -1,0,1,0 }, dy[] = { 0,1,0,-1 };

ll MAX(ll A, ll B) { return ((A) > (B) ? (A) : (B)); }
ll MIN(ll A, ll B) { return ((A) < (B) ? (A) : (B)); }
inline long long int xor128() {
	static long long int x = 123456789, y = 362436069, z = 521288629, w = 88675123;
	long long int t = (x ^ (x << 11));
	x = y; y = z; z = w;
	return (w = (w ^ (w >> 19)) ^ (t ^ (t >> 8)));
}

struct HashPair {

	//注意 constがいる
	template<class T1, class T2>
	size_t operator()(const pair<T1, T2>& p) const {

		//first分をハッシュ化する
		auto hash1 = hash<T1>{}(p.first);

		//second分をハッシュ化する
		auto hash2 = hash<T2>{}(p.second);

		//重複しないようにハッシュ処理
		size_t seed = 0;
		seed ^= hash1 + 0x9e3779b9 + (seed << 6) + (seed >> 2);
		seed ^= hash2 + 0x9e3779b9 + (seed << 6) + (seed >> 2);
		return seed;
	}
};

int main() {
	ll n, m, k;
	cin >> n >> m >> k;
	vector<vector<array<ll, 2>>> g((k + 1) * n);
	vector<ll> c(m);
	IN(c);
	LP(i, 0, m) {
		ll u, v;
		cin >> u >> v;
		--u, --v;
		LP(j, 0, k + 1) {
			g[j * n + u].push_back({ j * n + v,c[i] });
			g[j * n + v].push_back({ j * n + u,c[i] });
			if (j != k) {
				g[j * n + u].push_back({ (j+1) * n + v,0 });
				g[j * n + v].push_back({ (j+1) * n + u,0 });
			}
		}
	}
	priority_queue<array<ll, 2>, vector<array<ll, 2>>, greater<array<ll, 2>>> pq;
	vector<ll> d((k + 1)* n, LLONG_MAX);
	d[0] = 0;
	pq.push({ 0,0 });
	while (pq.size() != 0) {
		ll now = pq.top()[1], nd = pq.top()[0];
		pq.pop();
		if (d[now] != nd)continue;
		ALL(next, g[now]) {
			if (d[next[0]] > d[now] + next[1]) {
				d[next[0]] = d[now] + next[1];
				pq.push({ d[next[0]] ,next[0] });
			}
		}
	}
	ll ans = LLONG_MAX;
	LP(i, 0, k + 1)ans = min(ans, d[n * i + n - 1]);
	if (ans == LLONG_MAX)ans = -1;
	cout << ans;
}