#include<fstream>
using namespace std;
int d[5000010],v[5000010];
int main (){
ifstream f("deque.in");
ofstream h("deque.out");
int i,n,k,x=1,y=0;
long long s=0;
f>>n>>k;
for(i=1;i<=n;i++)
    f>>v[i];
for(i=1;i<=n;i++)
{
    while(x<=y&&v[i]<v[d[y]])y--;
    y++;
    d[y]=i;
    if(d[x]==i-k)x++;
    if(i>=k)s+=v[d[x]];
}
h<<s;
return 0;
}