#include <bits/stdc++.h>
#define deb cout << "in " << __LINE__ << "\t: "
using namespace std;
int n, a[100010], sum = 0, cnt[1000010], mx;
signed main() {
	ios::sync_with_stdio(false);
	cin.tie(0), cout.tie(0);
	cin >> n;
	priority_queue<int, vector<int>, greater<int>> s;
	for (int i = 1; i <= n; i++)
		cin >> a[i], cnt[a[i]]++, mx = max(mx, a[i]), s.push(i), sum += a[i];
	vector<pair<int, int>> ans;
	if (sum % 2) {
		for (int i = 1; i <= n; i++)
			if (a[i]) {
				ans.push_back({i, i});
				cnt[a[i]]--, cnt[--a[i]]++, sum--;
				while (!cnt[mx]) mx--;
				break;
			}
	}
	while (!s.empty() && mx * 2 < sum) {
		if (s.size() == 1) return 0;
		int x = s.top(); s.pop();
		int y = s.top(); s.pop();
		cnt[a[x]]--, cnt[--a[x]]++;
		cnt[a[y]]--, cnt[--a[y]]++;
		ans.push_back({x, y});
		sum -= 2;
		while (!cnt[mx]) mx--;
		if (a[x]) s.push(x);
		if (a[y]) s.push(y);
	}
	if (mx) {
		for (int i = 1; i <= n; i++)
			if (a[i] == mx) {
				for (int j = 1; j <= n; j++) {
					if (j == i) continue;
					while (a[j]--)
						ans.push_back({min(j, i), max(j, i)}), a[i]--;
				}
				while (a[i]--) ans.push_back({i, i});
				break;
			}
	}
	sort(ans.begin(), ans.end());
	cout << ans.size() << "\n";
	for (auto [x, y] : ans)
		cout << x << " " << y << "\n";
	return 0;
}