#include <iostream>
#include <fstream>
using namespace std;
ifstream fi("deque.in");
ofstream fo("deque.out");
int a[5000010],d[5000010],n,k,f,b;
long long s;
int main() {
    fi>>n>>k;
    for (int i=1;i<=n;i++)
        fi>>a[i];
    f=1,b=0;
    for (int i=1;i<=n;i++) {
        while (f<=b&&a[i]<=a[d[b]]) b--;
        d[++b]=i;
        if (d[f]==i-k) f++;
        if (i>=k) s+=a[d[f]];
    }
    fo<<s;
    return 0;
}