#include <fstream>

using namespace std;
ifstream cin("deque.in");
ofstream cout("deque.out");
int v[10000001];
int main()
{
    int n,k,minn,s=0;
    cin>>n>>k;
    for(int i=1;i<=n;i++)
        cin>>v[i];
    for(int i=1;i<=n-k+1;i++){
        minn=-10000001;
        for(int j=i;j<=i+k-1;j++){
            if(v[j]<minn)
                minn=v[j];
        }
        s=s+minn;
    }
    cout<<s;
    return 0;
}