#include <cstdio>
#include <deque>
#include <iostream>
#define nmax 5000005
using namespace std;
deque <int> p;
long long sum;
int n,k,x,v[nmax];

FILE *f=fopen("deque.in","r");
FILE *g=fopen("deque.out","w");

int main()
{
    int i,j;
    fscanf(f,"%d %d",&n,&k);
    for (i=1; i<=k; i++) {
        fscanf(f,"%d",&v[i]);
        while (!p.empty()&&v[i]<v[p.back()])
            p.pop_back();

        p.push_back(i);
        }
    sum+=v[p.front()];
    for (i=k+1;i<=n;i++) {
        while (!p.empty()&&i-p.front()>=k)
            p.pop_front();
        fscanf(f,"%d",&v[i]);
        while (!p.empty()&&v[i]<v[p.back()])
            p.pop_back();
        p.push_back(i);

        sum+=1LL*v[p.front()];
    }
    fprintf(g,"%lld\n",sum);
    return 0;
}