#include<bits/stdc++.h>
using namespace std;
#define int long long
int read(){
	int n=0,f=1;
	char ch=getchar();
	while(!isdigit(ch)){
		if(ch=='-')f=-1;
		ch=getchar();
	}
	while(isdigit(ch)){
		n=n*10+ch-'0';
		ch=getchar();
	}
	return n*f;
}
int n,k;
int a[1000005]; 
int dp[5005][5005];
signed main(){
	n=read(),k=read();
	for(int i=1;i<=n;i++)a[i]=read();
	memset(dp,-0x3f,sizeof(dp));
	dp[0][0]=0;
	for(int i=1;i<=n;i++){
		for(int j=0;j<=min(i,k);j++){
			//i-j
			dp[i][j]=max(dp[i][j],dp[i-1][j]+(a[i]==i-j));
			if(j)dp[i][j]=max(dp[i][j],dp[i-1][j-1]); 
		}
	}
	cout<<dp[n][k]<<"\n";
	return 0;
}