#include<cstdio>
#include<deque>
using namespace std;
int n,i,m,a[5000003];
long long s;
deque < int > cc;
int main()
{
freopen("deque.in","r",stdin);
freopen("deque.out","w",stdout);
scanf("%d",&n);
scanf("%d",&m);
for(i=1;i<=n;i++)
{
    scanf("%d",&a[i]);
    while(!cc.empty()&&a[cc.back()]>=a[i]) cc.pop_back();
    cc.push_back(i);
    if(cc.front()<=i-m) cc.pop_front();
    if(i>=m) s=s+a[cc.front()];
}
printf("%lld\n",s);
return 0;
}