#include <bits/stdc++.h>
using namespace std;
using ll = long long;
const ll mod = 1e9 + 7;
const int N = 200005;
const int INF = 0x3f3f3f3f;
int val[N << 2];
int a[N];
void build(int u, int l, int r) {
    if (l == r) {
        val[u] = a[l];
        return;
    }
    int mid = l + r >> 1;
    build(u << 1, l, mid);
    build(u << 1 | 1, mid + 1, r);
    val[u] = max(val[u << 1], val[u << 1 | 1]);
}
void update(int u, int l, int r, int x, int v) {
    if (l == r) {
        val[u] = v;
        return;
    }
    int mid = l + r >> 1;
    if (x <= mid) {
        update(u << 1, l, mid, x, v);
    } else {
        update(u << 1 | 1, mid + 1, r, x, v);
    }
    val[u] = max(val[u << 1], val[u << 1 | 1]);
}
int querymax() {
    return val[1];
}
int findmax(int u, int l, int r, int x) {
    if (val[u] < x) return -1;
    if (l == r) return l;
    int mid = l + r >> 1;
    if (val[u << 1] == x) {
        return findmax(u << 1, l, mid, x);
    } else {
        return findmax(u << 1 | 1, mid + 1, r, x);
    }
}
int n;
int findmaxidx() {
    return findmax(1, 1, n, val[1]);
}
int main() {
    cin >> n;
    ll s = 0;
    for (int i = 1; i <= n; i++) {
        cin >> a[i];
        s += a[i];
    }
    int mx = *max_element(a + 1, a + n + 1);
    int k = max((ll)mx, (s + 1) / 2);
    build(1, 1, n);
    set<int> pos;
    for (int i = 1; i <= n; i++) {
        if (a[i] > 0) pos.insert(i);
    }
    vector<pair<int, int>> ans;
    ll sum = s;
    for (int ss = 1; ss <= k; ss++) {
        int tmp = k - ss;
        int i = *pos.begin();
        vector<int> vec;
        vec.push_back(i);
        auto it = pos.begin();
        if (*it == i) {
            it++;
            if (it != pos.end()) vec.push_back(*it);
        }
        int pmax = findmaxidx();
        if (pmax != i) vec.push_back(pmax);
        sort(vec.begin(), vec.end());
        vec.erase(unique(vec.begin(), vec.end()), vec.end());
        bool ok = 0;
        for (auto j : vec) {
            int d = (i == j ? 1 : 2);
            int lai = a[i], laj = a[j];
            a[i]--;
            update(1, 1, n, i, a[i]);
            if (i != j) {
                a[j]--;
                update(1, 1, n, j, a[j]);
            }
            int now = querymax();
            ll nowsum = sum - d;
            if (now <= tmp && nowsum <= 2ll * tmp) {
                ans.push_back({i, j});
                sum = nowsum;
                if (a[i] == 0) pos.erase(i);
                if (i != j && a[j] == 0) pos.erase(j);
                ok = 1;
                break;
            }
            a[i] = lai;
            update(1, 1, n, i, lai);
            if (j != i) {
                a[j] = laj;
                update(1, 1, n, j, laj);
            }
        }
        assert(ok);
    }
    cout << (int)ans.size() << "\n";
    for (auto [x, y] : ans) {
        cout << x << " " << y << "\n";
    }
    return 0;
}