#include <fstream>
#include <cstdio>

#define NMax 5000005
using namespace std;

int n,k;
int a[NMax],q[NMax];

int main()
{
    freopen("deque.in","r",stdin);
    freopen("deque.out","w",stdout);
    scanf("%d%d",&n,&k);
    for(int i = 1; i <= n; ++i){
        scanf("%d",&a[i]);
    }
    long long s = 0;
    int fr = 1, bk = 0;
    for(int i = 1; i <= n; ++i){

        while(fr <= bk && a[i] <= a[q[bk]]){
            bk--;
        }
        q[++bk] = i;
        if(q[fr] == i - k){
            fr++;
        }
        if(i >= k)
            s += a[q[fr]];
    }
    printf("%lld",s);
    return 0;
}