#include <cstdio>
#include <deque>
#define MAX 5000100
using namespace std;
deque <int> dubla;
int n,k;
long long sol;
int v[MAX];
int main()
{
    freopen("deque.in","r",stdin);
    freopen("deque.out","w",stdout);
    scanf("%d%d",&n,&k);
    for(int i=1;i<=n;scanf("%d",v+i),++i);
    for(int i=1;i<=n;++i){
        while(!dubla.empty() and v[i]<=v[dubla.back()])dubla.pop_back();
        if(!dubla.empty() and i-k==dubla.front())dubla.pop_front();
        dubla.push_back(i);
        if(i>=k)sol=sol+v[dubla.front()];
    }
    printf("%lld\n",sol);
    return 0;
}