#include <bits/stdc++.h>

using namespace std;
ifstream f("deque.in");
ofstream g("deque.out");
int n,k,first,last,i;
long long s = 0;

int main()
{
    first = 0;
    last = -1;
    f>>n>>k;
    int deq[n] , v[n+1];
    for(i=0;i<n;i++)
        f>>v[i];
    for(i=0;i<n;i++)
    {
        while(first<=last and v[i]<v[deq[last]])
            last--;
        last++;
        deq[last] = i;
        if(deq[first] == i-k)
            first++;
        if(i>=k-1)
            s = s+v[deq[first]];
    }
    g<<s;
    return 0;
}