#include <fstream>

using namespace std;

long long int v[5000001],de[5000001];

int main(){
    long long int n,st,dr,sum,i,k;
    ifstream f("deque.in");
    ofstream g("deque.out");
    f>>n>>k;
    for(i = 1;i <= n;i++){
        f>>v[i];
    }
    st = 0;
    dr = sum = 0;
    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]];
        }
    }
    g<<sum;
    return 0;
}