#include <fstream>
using namespace std;

ifstream in ("deque.in"); ofstream out ("deque.out");
int d[5000010],a[5000010],n,k,f,l,i;
long long s;

int main () {
    in>>n>>k;
    for (i=0; i<n; i++) {
        in>>a[i];
        while (f<l&&a[d[l-1]]>=a[i]) l--;
        d[l++]=i;
        if (i-d[f]>=k) f++;
        if (i>=k-1) s+=a[d[f]];
    }
    out<<s<<"\n";
    return 0;
}