//yukicoder@cpp17

#include <iostream>
#include <iomanip>

#include <algorithm>

#include <cmath>
#include <cctype>
#include <climits>
#include <cassert>

#include <string>
#include <vector>
#include <set>
#include <stack>
#include <queue>
#include <map>

#include <random>

#include <bitset>

#include <complex>

#include <utility>

#include <numeric>

#include <functional>


using namespace std;
using ll = long long;
using P = pair<ll,ll>;


const ll MOD = 998244353;
const ll MODx = 1000000007;
const int INF = (1<<30)-1;
const ll LINF = (1LL<<62LL)-1;
const double EPS = (1e-10);


P ar4[4] = {{0,1},{0,-1},{1,0},{-1,0}};
P ar8[8] = {{-1,-1},{-1,0},{-1,1},{0,-1},{0,1},{1,-1},{1,0},{1,1}};


template <typename T> vector<T> make_vector(size_t a, T b) { return vector<T>(a, b); }
template <typename... Ts> auto make_vector(size_t a, Ts... ts) { return vector<decltype(make_vector(ts...))>(a, make_vector(ts...)); }
 
/*
確認ポイント
cout << fixed << setprecision(n) << 小数計算//n桁の小数表記になる

計算量は変わらないが楽できるシリーズ
min(max)_element(iter,iter)で一番小さい(大きい)値のポインタが帰ってくる
count(iter,iter,int)でintがiterからiterの間にいくつあったかを取得できる
*/

/* comment outed because can cause bugs
__attribute__((constructor))
void initial() {
  cin.tie(0);
  ios::sync_with_stdio(false);
}
*/

template< typename T, typename F>
struct SegmentTree{
  private:
    int n;
    vector<T> node;

    F f;
    T initer;

  public:
    SegmentTree(int n_, F f, T initer) : f(f),initer(initer) {
      n = 1;
      while(n < n_)n*=2;
      node.resize(2*n-1, initer);
    }

    SegmentTree(int n_, F f,T initer, vector<T> x) : f(f),initer(initer) {
      n = 1;
      while(n < n_)n*=2;
      node.resize(2*n-1, initer);
      set(x);
    }

    void set(vector<T> x){
      for(int i = 0; (int)x.size() > i; i++){
        update(i,x[i]);
      }
    }

    void update(int x, T val){
      x += (n-1);

      node[x] = val;

      while(x > 0){
        x = (x-1)/2;
        node[x] = f(node[2*x+1],node[2*x+2]);
      }
    }

    void add(int x, T val){
      x += (n-1);
      
      node[x] += val;
      while(x > 0){
        x = (x-1)/2;
        node[x] = f(node[2*x+1],node[2*x+2]);
      }
    }

    T getf(int a,int b, int k=0, int l=0, int r=-1){
      
      if(r < 0){
        r = n-1;
      }
      if(r < a || b < l){
        return initer;
      }
      if(a <= l && r <= b){
        return node[k];
      }

      T vl = getf(a,b,2*k+1,l,(l+r)/2);
      T vr = getf(a,b,2*k+2,(l+r)/2+1,r);
      return f(vl,vr);
    }

    void debug(){
      int nw = 1;
      int curr = 1;
      cout << "---begin---" << endl;
      for(int i = 0; 2*n-1 > i; i++){
        cout << node[i] << " ";
        if(nw == curr)cout << endl,nw *= 2, curr=1;
        else curr++;
      }
      cout << "---end---" << endl;
    }
};

template <typename T, typename F>
SegmentTree<T, F> get_segment_tree(int N, const F &f, T initer){
  return SegmentTree<T,F>{N,f,initer};
}

template <typename T, typename F>
SegmentTree<T, F> get_segment_tree(int N, const F &f, T initer, vector<T> x){
  return SegmentTree<T,F>{N,f,initer,x};
}
int dp[200010];

int main(){
  int n;cin>>n;
  vector<long long> A(n);
  vector<long long> B(n);
  for(int i = 0; n > i; i++){
    cin>>A[i],A[i]-=i;
    B[i] = A[i];
  }
  sort(B.begin(), B.end());
  B.erase(unique(B.begin(), B.end()), B.end());
  map<long long, long long> Bc;
  for(int i = 0; B.size() > i; i++){
    Bc[B[i]] = i;
  }
  auto seg = get_segment_tree(B.size(), [](long long a, long long b){return max(a,b);}, 0LL);
  for(int i = 0; n > i; i++){
    auto z = seg.getf(0, Bc[A[i]]);
    seg.update(Bc[A[i]], z+1);
  }
  cout << n-seg.getf(0, B.size()-1) << endl;
  
  return 0;
}