#include <fstream>

using namespace std;
int n,k,Min,s,a[5000005];
ifstream f("deque.in");
ofstream g("deque.out");
void citire()
{
    int i;
    f>>n>>k>>a[1];
    Min=a[1];
    for(i=2;i<=k;i++)
    {
        f>>a[i];
        if(Min>a[i])Min=a[i];
    }
    s+=Min;
}
int rezolvare()
{
    int i,j;
    Min=10000001;
    i=2;
    while(i<=n-k+1)
    {
        j=0;
        while(j<k)
        {
            if(j==k-1)
            {
                f>>a[i+j];
            }
            if(a[i+j]<Min)
                Min=a[i+j];
            j++;
        }
        i++;
        s+=Min;
        Min=10000001;
    }
    return s;
}
int main()
{
    citire();
    g<<rezolvare()<<'\n';
    return 0;
}