#include <iostream>
#include <cstdio>
#include <string.h>
#define inf 0x3f3f3f3f3f3f3f3f
using namespace std;

int n,k;
int v[5000010];
long long suma;
int j=1;
int front;
int main()
{
    freopen("deque.in","r",stdin);
    freopen("deque.out","w",stdout);
    scanf("%d%d",&n,&k);
    int x;
    memset(v,inf,sizeof(v));
    front=1;
    for (int i=1;i<=n;i++)
    {
        scanf("%d",&x);
        while (x<v[j] && j>=front)
        {
            v[j]=x;
            j--;
        }
        while (j<i){
        ++j;
        if (x<v[j])
            v[j]=x;
        }
        if (i>=k)
            suma+=v[front],front++;
    }
    printf("%lld",suma);
    return 0;
}