#include <bits/stdc++.h>
using namespace std;
typedef signed long long ll;

#undef _P
#define _P(...) (void)printf(__VA_ARGS__)
#define FOR(x,to) for(x=0;x<(to);x++)
#define FORR(x,arr) for(auto& x:arr)
#define ITR(x,c) for(__typeof(c.begin()) x=c.begin();x!=c.end();x++)
#define ALL(a) (a.begin()),(a.end())
#define ZERO(a) memset(a,0,sizeof(a))
#define MINUS(a) memset(a,0xff,sizeof(a))
//-------------------------------------------------------

int N;
int A[202020];
int V[202020];


void solve() {
	int i,j,k,l,r,x,y; string s;
	
	
	cin>>N;
	for(i=0;i<=N+1;i++) V[i]=1<<30;
	int ma=0;
	int left=0;
	for(i=1;i<=N;i++) {
		cin>>x;
		x-=i;
		if(x<0) continue;
		left++;
		y=lower_bound(V,V+N+1,x+1)-V;
		V[y]=x;
		ma=max(ma,y);
	}
	
	cout<<(N-left)+left-(ma+1)<<endl;
	
	
	
}


int main(int argc,char** argv){
	string s;int i;
	if(argc==1) ios::sync_with_stdio(false), cin.tie(0);
	FOR(i,argc-1) s+=argv[i+1],s+='\n'; FOR(i,s.size()) ungetc(s[s.size()-1-i],stdin);
	cout.tie(0); solve(); return 0;
}