#include <fstream>
using namespace std;
ifstream  fin("deque.in");
ofstream fout("deque.out");
int N,K,i,j,v[5000002],vmin;
long long s;
int main()
{
    fin>>N>>K;

    for(i=1; i<=N; i++)
    {
        fin>>v[i];
    }

    s=0;
    for(i=1; i<=N-K+1; i++)
    {
        vmin=100000000;
        for(j=i; j<=i+K-1; j++)
        {
            if(v[j]<vmin)
            {
                vmin=v[j];
            }
        }

        s+=vmin;
    }

    fout<< s;

    return 0;
}