#include <bits/stdc++.h>
using namespace std;
const int N=3010;
const int INF=0x3f3f3f3f;
typedef long long LL;
int a[N];
LL MIN = INF;
int main() {
    int n,m;
    cin>>n>>m;
    for (int i = 1; i <= n; i++) cin>>a[i];
    for (int i = 1; i <= n-m+1; i++) {
        LL sum =0;
        for (int j = 1; j < m; j++) sum+=a[i+j];
        MIN=min(MIN,sum);
    }
    cout<<MIN;
    return 0;
}