#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;
vector<int> V;

vector<int> LIS(vector<int>& v) {
	int i,N=v.size();
	vector<int> dp(N,1<<30),id(N);
	FOR(i,v.size()) {
		id[i] = lower_bound(dp.begin(),dp.end(),v[i]+1) - dp.begin(); //こうすると同じ値も許容する
		dp[id[i]] = v[i];
	}
	int nl = *max_element(id.begin(),id.end());
	vector<int> ret(nl+1);
	FOR(i,N) if(id[N-1-i] == nl) ret[nl--] = v[N-1-i];
	return ret;
}

void solve() {
	int i,j,k,l,r,x,y; string s;
	
	cin>>N;
	FOR(i,N) {
		cin>>x;
		V.push_back(x+N-i);
	}
	
	auto a=LIS(V);
	cout<<N-a.size()<<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;
}