#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, ord[N], dis[N];
vector<int> p[N];

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

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

#define VIT vector<int>::iterator

inline bool calc(int L, int l, int r, int d) {
	if (l > r) return 1;
	VIT it = lower_bound(p[d].begin(), p[d].end(), l);
	if (*it > r) return 0;
	int las = l;
	for (; it != p[d].end() && *it <= r; ++it) {
		addedge(L, *it);
		if (!calc(*it, las, *it - 1, d + 1)) return 0;
		las = *it + 1;
	} 
	return calc(las - 1, las, r, d + 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]) {
			if (rt) {
				puts("-1");
				return 0;
			}
			rt = i;
		}
	}
	if (!rt) puts("-1");
	else {
		int cnt = 0;
		for (int i = rt; i <= n; ++i) ord[++cnt] = i;
		for (int i = 1; i < rt; ++i) ord[++cnt] = i;
		for (int i = 1; i <= n; ++i) dis[i] = d[ord[i]];
		for (int i = 1; i <= n; ++i)
			p[dis[i]].push_back(i);
		for (int i = 1; i <= n; ++i) p[i].push_back(n + 1);
		if (calc(1, 2, n, 1)) 
			for (int i = 1; i < n; ++i) printf("%d %d\n", ord[fr[i]], ord[to[i]]);
		else puts("-1");
	}
	return 0;
}