#include <algorithm>
#include <cassert>
#include <cctype>
#include <cmath>
#include <cstdio>
#include <cstdlib>
#include <ctime>
#include <deque>
#include <functional>
#include <iomanip>
#include <iostream>
#include <list>
#include <map>
#include <queue>
#include <random>
#include <set>
#include <sstream>
#include <string>
#include <utility>
#include <vector>

#define REP(i,s,n) for(int i=(int)(s);i<(int)(n);i++)

using namespace std;
typedef long long int ll;
typedef vector<int> VI;
typedef vector<ll> VL;
typedef pair<int, int> PI;



int main(void) {
  int n;
  cin >> n;
  VL a(n);
  REP(i, 0, n) {
    cin >> a[i];
    a[i] -= i + 1;
  }
  // Coord compression
  map<ll, int> tbl;
  vector<ll> inv_tbl;
  {
    set<int> vals;
    vals.insert(0);
    REP(i, 0, n) {
      if (a[i] >= 0) {
      vals.insert(a[i]);
      }
    }
    inv_tbl = vector<ll>(vals.begin(), vals.end());
    sort(inv_tbl.begin(), inv_tbl.end());
    REP(i, 0, inv_tbl.size()) {
      tbl[inv_tbl[i]] = i;
    }
  }
  VL dp(200010);
  int m = tbl.size();
  REP(i, 0, n) {
    if (tbl.count(a[i])) {
      int idx = tbl[a[i]];
      REP(j, idx, m) {
	dp[j] = max(dp[j], j >= 1 ? dp[j - 1] : 0) + (j == idx ? 1 : 0);
      }
    }
  }
  cout << n - dp[m - 1] << endl;
}