#include<iostream>
#include<fstream>
using namespace std;
ifstream f("deque.in");
ofstream g("deque.out");

int a[5000010],deque[5000010],n,k,stg,drt,i;
long long s=0;

int main()
{  stg=1,drt=0;
    f>>n>>k;
    for(i=1;i<=n;i++)
    {f>>a[i];
        while(stg<=drt && a[i]<=a[deque[drt]])
        drt--;
        drt++; deque[drt]=i;
        if(deque[stg]==i-k) stg++;
        if(i>=k) s=s+a[deque[stg]];
    }
    g<<s;
    return 0;
}