#include <fstream>


int main() {
    std::ifstream fileIn("deque.in");
    std::ofstream fileOut("deque.out");
    int n, k, i, first = 0, last =-1;
    long long suma=0;

    int *vectr = new int[5000010];
    int *dQ = new int[5000010];
    fileIn >> n >> k;

    for(i=0; i < n; i++) {
        fileIn >> vectr[i];

        while(first <= last && vectr[i] <= vectr[dQ[last]]) {
            last --;

        }

        last ++;
        dQ[last] = i;

        if (dQ[first] == i-k) {
            first ++;
        }


        suma += (i >= k-1) ?  vectr[dQ[first]] : 0;


    }

    fileOut << suma;

    delete [] vectr;
    delete [] dQ;
    return 0;
}