#include <cstdio>

using namespace std;

long long int v[5000005],deque[5000005];

int main(){
    long long int n,front,back,sum,i,k;
    freopen("deque.in", "r", stdin);
    freopen("deque.out", "w", stdout);
    scanf("%lld %lld",&n,&k);
    for(i = 1;i <= n;i++){
        scanf("%lld",&v[i]);
    }
    front = 1;
    back = sum = 0;
    for(i = 1;i <= n;i++){
        while(front <= back && v[i] <= v[deque[back]]){
            back--;
        }
        deque[++back] = i;
        if(deque[front] == i-k){
            front++;
        }
        if(i >= k){
            sum += v[deque[front]];
        }
    }
    printf("%lld\n",sum);
    return 0;
}