#include <iostream>
#include <fstream>
using namespace std;

long long n,k,st=0,dr=-1,s=0;

long long v[500001],d[500001];

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



int main()
{
    f>>n>>k;
    for(int i=0;i<n;i++){
            f>>v[i];
            if(st<=dr && d[st]==i-k)st++;
            while(st<=dr && v[i]<=v[d[dr]])dr--;
            d[++dr]=i;
            if(i>=k-1)s+=v[d[st]];

    }
    g<<s;
    return 0;
}