#include <fstream>
using namespace std;
ifstream in ("deque.in");
ofstream out ("deque.out");
const long long N=5000001;
long long dq[N], minn[N];
int main()
{
    int n, i, k, j;
    long long minim, s=0;
    in>>n>>k;
    for (i=1; i<=n; i++)
        in>>dq[i];
    for (i=1; i<=n-k+1; i++)
    {
        minim=10000001;
        for (j=i; j<=i-1+k; j++)
            if (minim>=dq[j])
                minim=dq[j];
        minn[i]=minim;
    }
    for (i=1; i<=n-k+1; i++)
        s+=minn[i];
    out<<s<<'\n';
    return 0;
}