#include <bits/stdc++.h>
using namespace std;

const int nmax=5e7+2;
long long n,k,v[nmax];

ifstream in("deque.in");
ofstream out("deque.out");

void read(){

in>>n>>k;
for(int i=1;i<=n;i++)
in>>v[i];

}

long long s;
void solve(){
deque<int>d;

for(int i=1;i<=n;i++)
{
while(!d.empty()&&v[i]<=v[d.back()])
 d.pop_back();

 d.push_back(i);

 if(i-k==d.front()) d.pop_front();

 if(i>=k) s=s+v[d.front()];

}

out<<s;
}

int main(){
 read();
 solve();

 return 0;
}