#include <cstdio>
#define max 5000009
using namespace std;
int D[max],a[max];
int main(){
    int k,n,i,f,b,s;
    freopen("deque.in","r",stdin);
    freopen("deque.out","w",stdout);
    scanf("%d%d",&n,&k);
    for(i=1;i<=n;i++) scanf("%d",&a[i]);
    b = 0 ; f = 1; s = 0;
    for(i=1;i<=n;i++){
        while(b >= f && a[i] <= a[D[b]]) b--;
        D[++b] = i;
        if(D[f] == i-k) f++;
        if(i>=k) s+=a[D[f]];
    }
    printf("%lld\n",s);
    return 0;
}