#include<cstdio>#include<cstring>#include<cctype>#include<algorithm>using namespace std;#define rep(i,s,t) for(int i=s;i<=t;i++)#define dwn(i,s,t) for(int i=s;i>=t;i--)#define clr(x,c) memset(x,c,sizeof(x))int read(){	int x=0;char c=getchar();	while(!isdigit(c)) c=getchar();	while(isdigit(c)) x=x*10+c-‘0‘,c=getchar();	return x;}const int nmax=1e5+5;const int inf=0x7f7f7f7f;int dp[nmax],a[nmax];int main(){	int n=read(),u,v,d,cnt=0,ans=0;	rep(i,1,n){		u=read();		if(u-i<0) ans++;else a[++cnt]=u-i;	}	fill(dp+1,dp+cnt+1,inf);	rep(i,1,cnt){		v=upper_bound(dp+1,dp+cnt+1,a[i])-dp;dp[v]=a[i];	}	printf("%d\n",ans+cnt-(lower_bound(dp+1,dp+cnt+1,inf)-dp-1));	return 0;}