#include<bits/stdc++.h>
using namespace std;
inline int read(){char c=getchar(),f=0;int t=0;for(;c<'0'||c>'9';c=getchar())if(!(c^45))f=1;for(;c>='0'&&c<='9';c=getchar())t=(t<<1)+(t<<3)+(c^48);return f?-t:t;}
inline void write(int x){static int t[25];int tp=0;if(x==0)return(void)(putchar('0'));else if(x<0){putchar('-');x=-x;}while(x){t[tp++]=x%10;x/=10;}while(tp--){putchar(t[tp]+48);}}
int main()
{
	//freopen(".in","r",stdin);
	//freopen(".out","w",stdout);
	int n=read(),m=read(),a[3010],s=0,minn=1234567;
	for(int i=0;i<n;i++){
		a[i]=read();
	}
	for(int i=0;i<n-m;i++){
		s=0;
		for(int j=i;j<i+m;j++){
			s+=a[j];
		}
		if(s<minn)minn=s;
	}
	write(minn);
	return 0;
}