#include<bits/stdc++.h>
using namespace std;
#define open(x) freopen(x ".in", "r", stdin);freopen(x ".out", "w", stdout);

inline int read(){int f=1;int x=0;char c=getchar();while(c<'0'||c>'9'){if(c=='-'){f=-f;}c=getchar();}while(c>='0'&&c<='9'){x=(x<<1)+(x<<3)+(c^48);c=getchar();}return x*f;}
inline void wr(int x){if(x<0){putchar('-');x=-x;}if(x>9){wr(x/10);}putchar(x%10+'0');}

int f[5005][5005];
vector<int> a;

signed main(){
	int n = read();
	int k = read(); 
	a.reserve(n + 1);
	a.push_back(0);
	for(int i = 1 ; i <= n ; ++i){
		a.push_back(read());
	}
	for(int i = 1 ; i <= n ; ++i){
		for(int j = 0 ; j <= i && j <= k;++j){
			f[i][j] = max(f[i - 1][j] + (a[i] == i - j) , f[i-1][j-1]);
		}
	}
	wr(f[n][k]);
	return 0;
}