#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<=U)&&(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;       
}