#include<cstdio>
using namespace std;
int n,m,v[5000002],dec[5000002],p,u,i;
long long s;
int main()
{
    freopen("deque.in","r",stdin);
    freopen("deque.out","w",stdout);
    scanf("%d%d",&n,&m);
    for(i=1;i<=n;i++)scanf("%d",&v[i]);
    p=1;
    for(i=1;i<=n;i++)
    {
        while(p<=u && v[i] <= v[dec[u]])u--;
        u++;
        dec[u]=i;
        if(dec[p] == i-m)p++;
        if(i>=m)s+=v[dec[p]];
    }
    printf("%lld",s);
}