#include <fstream>
#include <vector>
#include <deque>
using namespace std;

ifstream fin("deque.in");
ofstream fout("deque.out");
int n, k, i, sf, inc;

int main()
{
    fin>> n >>k;
    int v[n+1];
    deque <int> dq;

    for(i = 1; i <= n; i++){ fin>>v[i]; dq.push_back(v[i]); }
    inc = 1; sf = 0;
    long long suma = 0;

    for(i = 1; i <= n; i++){

        while( inc <= sf && v[ dq[sf] ] >= v[i]) sf--;
        dq[++sf] = i;

        if( dq[inc] == i-k) inc++;
        if(i >= k) suma += v[ dq[inc] ];
    }

    fout<<suma;
    return 0;
}