#include<fstream>
using namespace std;
ifstream fin("deque.in");
ofstream fout("deque.out");
int v[5000001],d[5000001],i,p,u,n,k;
long long sum;
int main(){
    fin>> n >> k;
    for( i = 1; i <= n; i++ ){
        fin>>v[i];
    }
    p = 1;
    u = 1;
    d[1] = 1;
    for(i=2;i<=n;i++){
        while( p <= u && v[i] < v[ d[u] ] ){
            u--;
        }
        d[++u] = i;
        if(i - d[p] == k){
            p++;
        }
        if( i >= k ){
            sum += v[ d[p] ];
        }
    }
    fout<< sum;
    return 0;
}