#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;  
}