#include <bits/stdc++.h>
using namespace std;
long long bin_pow(long long a, long long b) {
  if (b == 0) return 1;
  if (b % 2 == 0) {
    long long t = bin_pow(a, b / 2);
    return t * t % 1000000007;
  } else
    return a * bin_pow(a, b - 1) % 1000000007;
}
vector<long long> a;
int main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  long long t = 1, n, m, k = 0, x = 0, y = 0, z = 0, sum = 0, l = 0, r = 0,
            ans = 0, mn = LLONG_MAX, mx = LLONG_MIN;
  cin >> n;
  a.resize(n);
  vector<pair<long long, long long> > d;
  stack<long long> s;
  for (int i = 0; i < n; i++) cin >> a[i];
  t = 0;
  for (int i = 0; i < n; i++) {
    if (a[i] < t) {
      while (a[i] != t) {
        x = s.top();
        s.pop();
        d.push_back({x, i});
        t--;
      }
    } else {
      while (a[i] != t) {
        s.push(i + 1);
        t++;
      }
    }
  }
  while (!s.empty()) {
    x = s.top();
    d.push_back({x, n});
    s.pop();
  }
  cout << d.size() << "\n";
  for (auto u : d) cout << u.first << " " << u.second << "\n";
  return 0;
}
