#include <fstream>
using namespace std;
ifstream f("deque.in");
ofstream g("deque.out");
int a[5000000],c[5000000],i,j,e,k,b,n;
long long s;
int main()
{
f>>n>>k;
b=1;e=0;
for (i=1;i<=n;i++)
f>>a[i];

for(i=1;i<=n;i++)
{
while (b<=e && a[i]<a[c[e]])e--;
e++;c[e]=i;
if (c[b]==i-k) b++;
if (i>=k) s=s+a[c[b]];
}
g<<s<<'\n';


    return 0;
}