#include <iostream>
#include <fstream>
#include <vector>

using namespace std;

ifstream f("deque.in");
ofstream g("deque.out");

int n,k;
long long int s=0;
int nr[5000005];
int poz[5000005];

int b=1,t=1;


int main()
{
    int i;
    f>>n>>k;
    for(i=1;i<=n;++i)
        f>>nr[i];
    for(i=1;i<=n;++i)
    {
        while(b<t && nr[i]<=nr[ poz[t-1]])
            --t;
        poz[t]=i;
        ++t;
        if(poz[b] == i-k)
            ++b;
        if(i>=k)
            s+=nr[poz[b]];
    }
    g<<s;
    return 0;
}