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


int main()
{ ifstream fin("deque.in");
ofstream fout("deque.out");
int n,k,i,p=0,u=0;
long long suma=0;
fin>>n>>k;
k--;
int v[n],poz[n];
for(i=0;i<n;i++)
{fin>>v[i];
poz[u]=i;

while(p<=u && v[i]<=v[poz[u]])
    u--;
if(poz[p]==poz[u]-k)
    {suma+=v[poz[p]];
        p++;
    }
u++;
}
suma+=v[poz[p]];
fout<<suma;


	return 0;
}