#include <fstream>
#define N 5000005
using namespace std;
int n,k,deque[N];
long long a[N],sol;
int main()
{ int st,dr,i;
ifstream f("deque.in"); f>>n>>k;
st=1; dr=0; sol=0;
for(i=1;i<=n;++i)
    {
    f>>a[i];
    while(st<=dr&&a[i]<=a[deque[dr]])--dr;
    deque[++dr]=i;
    if(deque[st]==i-k)++st;
    if(i>=k)sol+=a[deque[st]];
    }
f.close();
ofstream g("deque.out"); g<<sol; g.close();
return 0;
}