#include <fstream>



using namespace std;
ifstream in("deque.in");
ofstream out("deque.out");
int v[5000001];
int d[5000001];
int main()
{
    int n,i,k,p,u;
    long long suma=0;
in>>n>>k;
for(i=1; i<=n;i++)in>>v[i];
p=u=1;
d[1]=1;
if(k==1)suma+=v[1];
/// v[ d[p] ] < .......< v[ d[u] ]
for( i=2; i<=n; i++){
while( u>=p && v[d[u]]>=v[i])u--;
if(u>=p && d[p]< i-k+1 )p++; /// am scos primul element
/// v[i-k+1 ] ..... v[i]
u++;
d[u]=i;
if(i>=k)suma+=v[d[p]];



}
out<<suma;
return 0;
}