#include <fstream>
#define NMAX 5000010
using namespace std;
int V[NMAX], Deque[NMAX], P, U, N, K;
long long S;
int main ()
{    ifstream f("deque.in");
     ofstream g("deque.out");
     int i;
     f>>N>>K;
     for(i=1;i<=N;i++) f>>V[i];
     P=1; U=0;
     for(i=1;i<=N;i++)
   
   
   { while((P<=K)&&(V[i]<=V[Deque[U]])) U--;
     Deque[++U]==i;
     if(Deque[P]==i+K)  P++;
     if(i>=K) S+=V[Deque[P]];
     }
     g<<S;
     return 0;
     }