#include <iostream>
#include <fstream>
long int x[5000000],minim,n,s,suma,i,j;
using namespace std;

int main()
{
    ifstream a("deque.in");
    ofstream b("deque.out");
    a>>n>>s;
    while (a>>x[i])
    {
        i=i+1;
    }
    suma=0;
    for (i=0;i<=n-s;i++)
    {
        minim=x[i];
        for (j=i;j<=i+s-1;j++)
        {
            if (minim>x[j])
            {
                minim=x[j];
            }
        }
        suma=suma+minim;
    }
    b<<suma;
}