#include<fstream>
#define dim 5000003

using namespace std;
 
ifstream f("deque.in");
ofstream g("deque.out");
int pos[dim],h[2*dim],N,i,op,a[dim],n,x,cnt;long long sum;
inline int rs(int nod){
    return 2*nod+1;
}
inline int ls(int nod){
    return 2*nod;
}
void urca(int k){
 
    while( k>1 && a[h[k/2]]>a[h[k]]){
        swap(pos[h[k]],pos[h[k/2]]);
        swap(h[k],h[k/2]);
        k/=2;
    }
}
void coboara( int nod){
 
    int fiu=nod;
 
 
 
    if(ls(nod)<=N && a[h[fiu]]>a[h[ls(nod)]] ){
        fiu=ls(nod);
 
    }
    if(rs(nod)<=N && a[h[fiu]]>a[h[rs(nod)]]){
        fiu=rs(nod);
    }
    if(nod!=fiu){
        swap(pos[h[nod]],pos[h[fiu]]);
        swap(h[fiu],h[nod]);
        coboara(fiu);
    }
}
void insert(    int X   ){
    h[++N]=X;
    pos[X]=N;
    urca(pos[X]);
}
 
void erase( int X ){
	
    swap(pos[h[X]],pos[h[N]]);
    swap(h[X],h[N]);
    --N;
    coboara(X);
	
}
int main () {
 int k,n;
    f>>n>>k;
	for(i=1;i<k;++i){
		
		f>>a[i];
		insert(i);
		
	}
	for(i=k;i<=n;++i){
		f>>a[i];
		insert(i);
		while(h[1]<i-k+1)
			erase(1);
		sum+=a[h[1]];
	}
	g<<sum<<"\n";
    return 0;
}