#include <map>
#include <set>
#include <list>
#include <cmath>
#include <queue>
#include <stack>
#include <cstdio>
#include <string>
#include <vector>
#include <complex>
#include <cstdlib>
#include <cstring>
#include <numeric>
#include <sstream>
#include <iostream>
#include <algorithm>
#include <functional>
  
#define mp       make_pair
#define pb       push_back
#define all(x)   (x).begin(),(x).end()
#define rep(i,n) for(int i=0;i<(n);i++)
  
using namespace std;
  
typedef    long long          ll;
typedef    unsigned long long ull;
typedef    vector<bool>       vb;
typedef    vector<int>        vi;
typedef    vector<vb>         vvb;
typedef    vector<vi>         vvi;
typedef    pair<int,int>      pii;
  
const int INF=1<<30;
const double EPS=1e-9;
  
const int dx[]={1,0,-1,0,1,1,-1,-1},dy[]={0,-1,0,1,1,-1,-1,1};

int LIS(vector<int> &A) {
  int N = A.size();
  vector<int> dp;
  for (int i = 0; i < N; i++) {
    int k = lower_bound(dp.begin(), dp.end(), A[i]) - dp.begin();
    if (dp.size() == k) {
      dp.push_back(A[i]);
    } else {
      dp[k] = A[i];
    }
  }
  return dp.size();
}

int main() {
  int N;
  cin >> N;
  vector<int> A(N);
  for (int i = 0; i < N; i++) {
    cin >> A[i];
  }
  vector<int> B;
  for (int i = 0; i < N - 1; i++) {
    if (A[i] - i < 0) continue;
    B.push_back(A[i] - i);
  }
  cout << N - LIS(B) << endl;

  return 0;
}