#include <fstream>
using namespace  std;
ifstream f("deque.in");
ofstream g("deque.out");
int a[5000000];
int v[5000000];
int main() {
int x,n,k;
long long s=0;
f>>n>>k;
for(int i = 0 ; i < n ;++i)
    f>>a[i];
int st= 0 ;
int dr = -1;
for(int i = 0; i <n ; ++i)
{
    while(st<=dr && a[i] < a[v[dr]])
        dr--;
    v[++dr] = i;
    if(v[st] == i - k)
        st++;
    if(i+1>=k)
        s+=a[v[st]];
}
g<<s;

    return 0;
}