#include <bits/stdc++.h>

using namespace std;

const int N = 5e5 + 5;

inline int read() {
	register int s = 0, f = 1; register char ch = getchar();
	while (!isdigit(ch)) f = (ch == '-' ? -1 : 1), ch = getchar();
	while (isdigit(ch)) s = (s * 10) + (ch & 15), ch = getchar();
	return s * f;
}

int n, d[N], fr[N], to[N], top = 0;

inline void addedge(int from, int t) {
	fr[++top] = from; to[top] = t;
}

inline int abs_(int a) {
	return a < 0 ? -a : a;
}

inline bool calc(int L, vector<int> p) {
	vector<int> q; int t = -1;
	bool res = 1;
	for (int i : p) {
		if (d[i] == d[L] + 1) {
			addedge(L, i); t = i;
			if (!q.empty()) {
				res &= calc(i, q);
				if (!res) return 0;
			}
			q.clear();
		} else q.push_back(i);
	} if (!q.empty()) {
		if (t == -1) return 0;
		return calc(t, q);
	} return 1;
}

int main() {
	n = read();
	for (int i = 1; i <= n; ++i) d[i] = read();
	int rt = 0;
	for (int i = 1; i <= n; ++i) {
		if (!d[i]) rt = i;
	}
	if (!rt) puts("-1");
	else {
		vector<int> p;
		for (int i = rt + 1; i <= n; ++i)
			p.push_back(i);
		for (int i = 1; i < rt; ++i)
			p.push_back(i);
		if (!calc(rt, p)) puts("-1");
		else {
			for (int i = 1; i < n; ++i)
				printf("%d %d\n", fr[i], to[i]);
		}
	}
	return 0;
}