#include<bits/stdc++.h>
using namespace std;
using Int = long long;
template<typename T1,typename T2> inline void chmin(T1 &a,T2 b){if(a>b) a=b;}
template<typename T1,typename T2> inline void chmax(T1 &a,T2 b){if(a<b) a=b;}

//INSERT ABOVE HERE
signed main(){
  Int n;
  cin>>n;
  vector<Int> a(n);
  for(Int i=0;i<n;i++) cin>>a[i];

  const Int INF = 1e15;
  vector<Int> lis(n+1,INF);
  for(Int i=0;i<n;i++){
    a[i]-=i+1;
    if(a[i]<0) continue;
    Int k=upper_bound(lis.begin(),lis.end(),a[i])-lis.begin();
    lis[k]=a[i];
  }
  
  Int ans=0;
  while(lis[ans]<INF) ans++;
  cout<<n-ans<<endl;
  return 0;
}