#include <cstdio>

using namespace std;

int v[5000001],de[5000001];
long long int n,st,dr,sum,i,k;
freopen("deque.in", "r", stdin);
freopen("deque.out", "w", stdout);

int main(){
    scanf("%lld %lld",&n,&k);
    for(i = 1;i <= n;i++){
        scanf("%d",&v);
    }
    for(i = 1;i <= n;i++){
        while(st <= dr && v[i] <= v[de[dr]]){
            dr--;
        }
        de[++dr] = i;
        if(de[st] == i-k){
            st++;
        }
        if(i >= k){
            sum += v[de[st]];
        }
    }
    printf("%lld",sum);
    return 0;
}