#include <iostream>
#include <algorithm>

using namespace std;

const int INF = 1<<30;
int n;
int a[200000];
int dp[200000];

int main(int argc, char *argv[])
{
  cin >> n;
  for (int i = 0; i < n; i++) {
    cin >> a[i];
    a[i] -= i;
  }

  fill(dp, dp + n, INF);
  for (int i = 0; i < n; i++) {
    if (a[i] > 0)
      *upper_bound(dp, dp + n, a[i]) = a[i];
  }

  int ret = lower_bound(dp, dp + n, INF) - dp;
  cout << n - ret << endl;
  
  return 0;
}