#include<stdio.h>
int a[3005],sum=0;
int main()
{
    int n,m,i,x,min;
    scanf("%d %d", &n, &m);
    for (i = 1; i <= n; i++)
    {
        scanf("%d", &a[i]);
    }
    for (i = 1; i <= n-m; i++)
    {
        x = i;
        for (int j = 1; j <= m; j++)//加m次
        {
            sum += a[i];
            i++;
        }
        i = x;
        if (i == 1)min = sum;
        if (sum < min)min = sum;
        sum = 0;
    }
    printf("%d", min);
    return 0;
}