#include <bits/stdc++.h>
#include "unistd.h"
using namespace std;
#define WA cout<<"char134217728";exit(0)
#define RE throw
#define TLE sleep(1000)
#define FOR(i,a,b) for(int i=(a),i##formax=(b);i<i##formax;i++)
#define FORR(i,a,b) for(int i=(a),i##formax=(b);i>=i##formax;i--)
#define pb push_back
#define mp make_pair
#define fi first
#define se second
#define pcnt __builtin_popcount
#define sz(x) (int)(x).size()
#define maxs(x,y) x=max(x,y)
#define mins(x,y) x=min(x,y)
#define show(x) cout<<#x<<" = "<<x<<endl;
#define all(a) (a.begin()),(a.end())
#define each(it,c) for(__typeof((c).begin()) it=(c).begin();it!=(c).end();it++)
#define perm(c) sort(all(c));for(bool c##p=1;c##p;c##p=next_permutation(all(c)))
#define uniq(v) sort(all(v));v.erase(unique(all(v)), v.end());
#define bit(n) (1LL<<(n))
#define randInt(l,r) (uniform_int_distribution<ll>(l,r)(rnd))
#define randDouble(l,r) (uniform_real_distribution<double>(l,r)(rnd))
#define dout(d) printf("%.12f\n",d)

typedef long long ll;
typedef __int128_t lll;
typedef pair<int,int> pii;
typedef pair<ll,ll> pll;
template<class T>using V=vector<T>;
template<class T>using VV=V<V<T>>;
template<class T,class Y>ostream& operator<<(ostream& o,const pair<T,Y>& p){return o<<"("<<p.fi<<", "<<p.se<<")";}
template<typename A,size_t N,typename T>void Fill(A (&array)[N],const T&v){fill((T*)array,(T*)(array+N),v);}
lll gcd(lll a,lll b,lll &x,lll &y){if(!b){x=1;y=0;return a;}lll d=gcd(b,a%b,y,x);y-=a/b*x;return d;}
ll gcd(ll a,ll b){lll x=0,y=0;return gcd(a,b,x,y);}
ll modInv(ll a,ll m){lll x,y;gcd(a,m,x,y);return (x%m+m)%m;}
ll modPow(lll a,lll n,ll m){if(!a)return a;lll p=1;for(;n>0;n>>=1,a=a*a%m)if(n&1)p=p*a%m;return(ll)p;}
bool isPrime(ll n){if(n<2||n%2==0)return n==2;lll t=n-1,d=t/(t&-t);for(lll a:{2,325,9375,28178,450775,9780504,1795265022})if(a%n){for(t=d,a=modPow(a,t,n);t!=n-1&&a!=1&&a!=n-1;a=a*a%n,t=t*2%n);if(a!=n-1&&t%2==0)return 0;}return 1;}
const int IINF = 1e9+6;
const ll LINF = 1e18;
const int MOD = 1e9+7;
const double PI = acos(-1);
const double EPS = 1e-10;
static random_device rd;
static mt19937 rnd(rd());

const int N = 1e5;
struct Seg{
  typedef ll T;
  const T e = 0;
  void merge(const T &a, const T &b, T &c){
    c = max(a, b);
  }

  int n;
  vector<T> d;

  void init(int m){
    n = 1<<(32-__builtin_clz(m-1));
    d = vector<T>(2*n, e);
  }
  void init(vector<T> &v){
    init(v.size());
    FOR(j, 0, v.size()) d[j+n] = v[j];
    for(int k=n-1;k>0;k--) merge(d[k*2], d[k*2+1], d[k]);
  }
  void update(int k, T a){
    k+=n;
    d[k]=a;
    while(k){
      k >>= 1;
      merge(d[k*2], d[k*2+1], d[k]);
    }
  }
  T query(int L, int R) {
    L += n; R += n;
    T l=e, r=e;
    while (L < R) {
      if (L & 1) merge(l, d[L++], l);
      if (R & 1) merge(d[--R], r, r);
      L >>= 1; R >>= 1;
    }
    merge(l, r, l);
    return l;
  }
  T get(int a){
    return d[n+a];
  }
} seg;
V<ll> Z, A;
int n;
main(){
  cin.tie(0);
  ios::sync_with_stdio(false);
  cin >> n;
  FOR(i, 0, n){
    ll a;
    cin >> a;
    a -= i;
    A.pb(a);
  }
  Z = A;
  Z.pb(IINF);
  uniq(Z);
  seg.init(sz(Z));
  for(ll a:A){
    if(a <= 0) continue;
    int i = lower_bound(all(Z), a)-Z.begin();
    seg.update(i, seg.query(0, i+1)+1);
  }
  cout << n-seg.query(0, sz(Z)) << endl;
}