#include<iostream>
using namespace std;
int main(){
    int n = 0,m = 0,a[100000] = {0},sum = 0,minNum = 100000;
    int cnt = 0;
    cin >> n >> m;
    for(int i = 1;i <= n;i++){
        cin >> a[i];
    }
    for(int j = 1;j <= n;j++){
        sum += a[j];
        cnt++;
        if(cnt == m){
            if(sum < minNum) minNum = sum;
            j = j - m + 1;
            cnt = 0;
            sum = 0;
        }
    }
    cout << minNum;
    return 0;
}