#include <bits/stdc++.h>
#define maxn 5000010
using namespace std;
int d[maxn],a[maxn],N,K,i;
long long s=0;
ifstream f("deque.in");
ofstream g("deque.out");
int main()
{
    f>>N>>K;
    for(i = 1; i <=N; i++)
        f>>a[i];
    int pr = 0;
    int ul = -1;
    for( i = 1; i <=N; i++)
    {
        int x = a[i];
        while(pr <=ul && a[d[ul]] >=x) ul--;
        d[++ul] = i;
        if(d[pr]==i-K) pr++;
        if(i>=K) s+=a[d[pr]];
    }
    g<<s;

    return 0;
}