#include <stdio.h>
#include <stdlib.h>

int v[5000000], d[5000000];

int main(){
    FILE *fin, *fout;
    int n, k, i, st, dr;
    long long s;
    fin=fopen("deque.in", "r");
    fout=fopen("deque.out", "w");
    fscanf(fin, "%d%d", &n, &k);
    st=0;
    dr=-1;
    s=0;
    for(i=0;i<n;i++){
        fscanf(fin, "%d", &v[i]);
        if(st<=dr && d[st]==i-k)
            st++;
        while(st<=dr && v[i]<=v[d[dr]])
            dr--;
        d[++dr]=i;
        if(i>=k-1){
            s+=(long long)v[d[st]];
            //printf("%lld\n", (long long)v[d[st]]);
        }
    }
    fprintf(fout, "%lld", s);
    fclose(fin);
    fclose(fout);

    return 0;
}