#include <iostream>
#include <deque>
using namespace std;
int A[10001],N,k,i=0,s=0,Min;
deque <int> deq;

int main()
{
    cin>>N>>k;
    for(int j=0;j<N;j++)
    {
        cin>>A[j];
    }
    while(i<=N-k)
    {
        Min=A[i];
        for(int j=0;j<k;j++)
        {
            if(A[i+j]<Min)
            {
                Min=A[i+j];

            }
        }
        s=s+Min;
        i++;
    }
    cout<<s;
    return 0;
}