#define _CRT_SECURE_NO_WARNINGS

#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <cmath>
#include <limits>
#include <ctime>
#include <cassert>
#include <map>
#include <set>
#include <iostream>
#include <memory>
#include <string>
#include <vector>
#include <algorithm>
#include <functional>
#include <sstream>
#include <stack>
#include <queue>
#include <numeric>
#include <iterator>
#include <bitset>
#include <unordered_map>
#include <unordered_set>

using namespace std;
#define FOR(i,n) for(int i = 0; i < (n); i++)
#define sz(c) ((int)c.size())
#define ten(n) ((int)1e##n)
using ll = long long;
using Pii = pair<int, int>;
using Pll = pair<ll, ll>;

template<typename ...> static inline int getchar_unlocked(void) { return getchar(); }
template<typename ...> static inline void putchar_unlocked(int c) { putchar(c); }
#define mygc(c) (c)=getchar_unlocked()
#define mypc(c) putchar_unlocked(c)
void reader(int& x) { int k, m = 0; x = 0; for (;;) { mygc(k); if (k == '-') { m = 1; break; }if ('0' <= k&&k <= '9') { x = k - '0'; break; } }for (;;) { mygc(k); if (k<'0' || k>'9')break; x = x * 10 + k - '0'; }if (m) x = -x; }
void reader(ll& x) { int k, m = 0; x = 0; for (;;) { mygc(k); if (k == '-') { m = 1; break; }if ('0' <= k&&k <= '9') { x = k - '0'; break; } }for (;;) { mygc(k); if (k<'0' || k>'9')break; x = x * 10 + k - '0'; }if (m) x = -x; }
int reader(char c[]) { int i, s = 0; for (;;) { mygc(i); if (i != ' '&&i != '\n'&&i != '\r'&&i != '\t'&&i != EOF) break; }c[s++] = i; for (;;) { mygc(i); if (i == ' ' || i == '\n' || i == '\r' || i == '\t' || i == EOF) break; c[s++] = i; }c[s] = '\0'; return s; }
int reader(string& c) { int i; for (;;) { mygc(i); if (i != ' '&&i != '\n'&&i != '\r'&&i != '\t'&&i != EOF) break; }c.push_back(i); for (;;) { mygc(i); if (i == ' ' || i == '\n' || i == '\r' || i == '\t' || i == EOF) break; c.push_back(i); }; return sz(c); }
template <class T, class S> void reader(T& x, S& y) { reader(x); reader(y); }
template <class T, class S, class U> void reader(T& x, S& y, U& z) { reader(x); reader(y); reader(z); }
template <class T, class S, class U, class V> void reader(T& x, S& y, U& z, V & w) { reader(x); reader(y); reader(z); reader(w); }
void writer(int x, char c) { int s = 0, m = 0; char f[10]; if (x<0)m = 1, x = -x; while (x)f[s++] = x % 10, x /= 10; if (!s)f[s++] = 0; if (m)mypc('-'); while (s--)mypc(f[s] + '0'); mypc(c); }
void writer(ll x, char c) { int s = 0, m = 0; char f[20]; if (x<0)m = 1, x = -x; while (x)f[s++] = x % 10, x /= 10; if (!s)f[s++] = 0; if (m)mypc('-'); while (s--)mypc(f[s] + '0'); mypc(c); }
void writer(const char c[]) { int i; for (i = 0; c[i] != '\0'; i++)mypc(c[i]); }
void writer(const string& x, char c) { int i; for (i = 0; x[i] != '\0'; i++)mypc(x[i]); mypc(c); }
void writer(const char x[], char c) { int i; for (i = 0; x[i] != '\0'; i++)mypc(x[i]); mypc(c); }
template<class T> void writerLn(T x) { writer(x, '\n'); }
template<class T, class S> void writerLn(T x, S y) { writer(x, ' '); writer(y, '\n'); }
template<class T, class S, class U> void writerLn(T x, S y, U z) { writer(x, ' '); writer(y, ' '); writer(z, '\n'); }
template<class T, class S, class U, class V> void writerLn(T x, S y, U z, V v) { writer(x, ' '); writer(y, ' '); writer(z, ' '); writer(v, '\n'); }
template<class T> void writerArr(T x[], int n) { if (!n) { mypc('\n'); return; }FOR(i, n - 1)writer(x[i], ' '); writer(x[n - 1], '\n'); }
template<class T> void writerArr(vector<T>& x) { writerArr(x.data(), (int)x.size()); }

template<class T> void chmin(T& a, const T& b) { if (a > b) a = b; }
template<class T> void chmax(T& a, const T& b) { if (a < b) a = b; }

template<class T> T gcd(T a, T b) { return b ? gcd(b, a % b) : a; }
template<class T> T lcm(T a, T b) { return a / gcd(a, b) * b; }
ll mod_pow(ll a, ll n, ll mod) {
	ll ret = 1;
	ll p = a % mod;
	while (n) {
		if (n & 1) ret = ret * p % mod;
		p = p * p % mod;
		n >>= 1;
	}
	return ret;
}
template<class T> T extgcd(T a, T b, T& x, T& y) { for (T u = y = 1, v = x = 0; a;) { T q = b / a; swap(x -= q * u, u); swap(y -= q * v, v); swap(b -= q * a, a); } return b; }
ll mod_inv(ll a, ll m) { ll x, y; extgcd<ll>(a, m, x, y); return (m + x % m) % m; }

#ifdef _MSC_VER
template <typename ... Args>
void debugPrintf(const char *format, Args const & ... args) {
	fprintf(stderr, format, args ...);
	fflush(stderr);
}
#else
#define debugPrintf(...)
#endif

vector<int> solve(int k, vector<int> a) {
	int n = sz(a);
	if (n == 2) {
		vector<int> ans = { 0, 1 };
		FOR(i, k) ans.push_back(i % 2);
		int zeroC = (k + 1) / 2 + 1;
		int oneC = k + 2 - zeroC;
		if (zeroC > a[0] || oneC > a[1]) {
			for (auto& c : ans) c = 1 - c;
			swap(zeroC, oneC);
		}
		if (zeroC > a[0] || oneC > a[1]) {
			return {};
		} else {
			return ans;
		}
	}

	vector<Pii> rems;
	int sm = 0;
	FOR(i, n) {
		int diff = k + 1 - a[i];
		if (diff > 0) {
			rems.emplace_back(diff, i);
			sm += diff;
		}
	}
	if (sm > k) {
		return {};
	}

	vector<int> lasts(k, -1);
	sort(rems.rbegin(), rems.rend());
	int ni = 0;
	for (auto& kv : rems) {
		FOR(j, kv.first) {
			lasts[ni] = kv.second;
			ni += 2;
			if (ni >= k) {
				ni -= k;
				if (ni % 2 == 0) ni++;
			}
		}
	}

	FOR(i, k - 1) {
		if (lasts[i] == lasts[i + 1] && lasts[i] != -1) {
			return {};
		}
	}
	FOR(i, k) {
		if (lasts[i] != -1) continue;
		int use = 0;
		for (; use < n; use++) {
			if (i > 0 && use == lasts[i - 1]) continue;
			if (i < sz(lasts) - 1 && use == lasts[i + 1]) continue;
			break;
		}
		lasts[i] = use;
	}

	vector<int> ret;
	FOR(i, n) if(i != lasts[0]) ret.push_back(i);
	ret.push_back(lasts[0]);
	FOR(i, k) {
		int nxt = -1;
		if (i != k - 1) nxt = lasts[i + 1];
		FOR(j, n) if (lasts[i] != j && j != nxt) {
			ret.push_back(j);
		}
		if (nxt != -1) ret.push_back(nxt);
	}

	return ret;
}

bool verify(vector<int> a, vector<int>& ans, int k) {
	FOR(i, sz(ans)) a[ans[i]]--;
	FOR(i, sz(a)) if (a[i] < 0) return false;

	vector<int> memo(sz(ans), ten(5));
	{
		bool used[50] = {};
		FOR(i, sz(ans)) if (!used[ans[i]]) {
			used[ans[i]] = true;
			memo[i] = 0;
		}
	}
	FOR(s, sz(ans)) {
		bool used[50] = {};
		for (int i = s + 1; i < sz(ans); i++) if (!used[ans[i]]) {
			used[ans[i]] = true;
			memo[i] = min(memo[i], memo[s] + 1);
		}
	}
	int mn = ten(5);
	{
		bool used[50] = {};
		for (int i = sz(ans) - 1; i >= 0; i--) {
			if (!used[ans[i]]) {
				used[ans[i]] = true;
				mn = min(mn, memo[i] + 1);
			}
		}
	}

	return mn >= k;
}

void test() {
	int n = 3;
	for (int k = 1; k <= 5; k++) {
		FOR(a, 10) FOR(b, 10) FOR(c, 10) {
			vector<int> x = { a,b,c };
			auto ans = solve(k, x);
			if (sz(ans) == 0) {
				continue;
			}
			bool ok = verify(x, ans, k);
			if (!ok) {
				cout << "?";
			}
		}
	}
}

int main() {
	// test();

	int n, k; reader(n, k);
	vector<int> a(n);
	FOR(i, n) reader(a[i]);


	vector<int> ans = solve(k, a);
	if (sz(ans) == 0) {
		writerLn(-1);
	} else {
		writerLn(sz(ans));
		for (auto& c : ans) c++;
		writerArr(ans);
	}



	return 0;
}

Measured memory_bytes: 256