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#include<iostream>
using namespace std;
long long n,k,sum=0,b[1000005];
long long a[1000005];
int main(){
	
	cin >> n>>k;
	for(int i=1;i<n;i++){
		cin >> a[i]; 
	}
	long long tr = 0;
	b[0] = 0;
	b[1] = a[1]; 
	for(int i=2;i<n;i++){
		b[i] = b[i-1] + a[i];
 	}
 	for(int i=0;i<n;i++){
 		if(i+k>n-1){
 			if(b[n-1]-b[i]>tr) tr = b[n-1]-b[i];
		}
 		else if(b[i+k]-b[i] > tr) tr = b[i+k]-b[i];
	}
	cout << b[n-1]-tr << endl;
	return 0;
}