#include<bits/stdc++.h>
using namespace std;
#define FOR(i,a,b) for (int i=(a);i<(b);i++)
#define RFOR(i,a,b) for (int i=(b)-1;i>=(a);i--)
#define REP(i,n) for (int i=0;i<(n);i++)
#define RREP(i,n) for (int i=(n)-1;i>=0;i--)
typedef long long LL;
LL A[200001];
LL B[200011];
int N;

int binary_serach(LL x){
	int lb=-1;
	int ub=200010;
	while(ub-lb>1){
		int mid=(ub+lb)/2;
		if(B[mid]>x){
			ub=mid;
		}else{
			lb=mid;
		}
	}
	return ub;
}

int main(){
	cin>>N;
	REP(i,N){
		cin>>A[i];
		A[i]-=i;
	}
	REP(i,200011){
		B[i]=1e12;
	}
	REP(i,N){
		int b=binary_serach(A[i]);
		B[b]=A[i];
		/*cout<<"test"<<endl;
		REP(j,10){
			cout<<B[j]<<endl;
		}*/
	}
	int ans=0;
	REP(i,200011){
		if(B[i]!=1e12)ans++;
	}
	cout<<N-ans<<endl;
	return(0);
}