#include<stdio.h>
using namespace std;

#define nmax 5000005

int n,k,v[nmax],d[nmax],f,b;
long long s;

void citire()
{
    scanf("%d%d",&n,&k);
    for(int i=1;i<=n;++i) scanf("%d",&v[i]);
}

void solve()
{
    for(int i=1;i<=k-1;++i)
        d[i]=1;
    f=1;
    b=k;
    for(int i=k;i<=n;++i)
    {
        while(v[f]>=v[i] &&f<i ) f++;
        s+=v[f];
        if(i-f>=k-1)
        f++;
    }
    printf("%lld",s);
}

int main()
{
    freopen("deque.in","r",stdin);
    freopen("deque.out","w",stdout);
    citire();
    solve();
}