#include<iostream>
#include<fstream>
#include<deque>
using namespace std;
ifstream f("deque.in");
ofstream g("deque.out");
int n,prim=1,ult,suma,k;
int main()
{
    int min1;
    deque<int>v;
    f>>n>>k;
    int x;
    for(int i=1;i<=n;i++)
    {
        f>>x;
        if(ult-prim+1<k)
        {
            ult++;
            v.push_back(x);
        }
        else if(ult-prim==k-1)
        {
            ult++;
            prim++;
            v.push_back(x);
        }
        if(ult-prim==k-1)
        {
            min1=v[prim];
            for(int i=prim+1;i<=ult;i++)
            {
                if(min1>v[i])
                    min1=v[i];
            }
            suma=suma+min1;
        }
    }
    g<<suma;
}