package main

import "fmt"

func main() {
    var n, m int
    fmt.Scanf("%d %d", &n, &m)
    
    if m == 0 || n == 0 {
        fmt.Println(0)
        return
    }

    arr := make([]int, n)
    result := make([]int, n)

    // 输入数组
    for i := 0; i < n; i++ {
        fmt.Scan(&arr[i])
    }

    // 计算前缀和 + 滑动窗口
    result[0] = arr[0]
    for i := 1; i < n; i++ {
        if i < m {
            result[i] = result[i - 1] + arr[i]
        } else {
            result[i] = result[i - 1] + arr[i] - arr[i - m]
        }
    }

    min := result[m - 1]
    for i := m; i < n; i++ {
        if result[i] < min {
            min = result[i]
        }
    }

    fmt.Printf("%d\n", min)
}