#include <stdio.h>
#define MAXN 5000000
int v[MAXN], dq[MAXN];
int main(){
    int n, k, i, st, dr;
    long long ans;
    FILE *fin, *fout;
    fin=fopen("deque.in", "r");
    fout=fopen("deque.out", "w");
    fscanf(fin, "%d%d", &n, &k);
    for(i=0; i<n; i++){
        fscanf(fin, "%d", &v[i]);
    }
    ans=0;
    st=0;
    dr=0;
    for(i=0; i<n; i++){
        if(i-dq[st]>=k){
            st++;
        }
        while((dr>st)&&(v[dq[dr-1]]>=v[i])){
            dr--;
        }
        dq[dr++]=i;
        if(i>=k-1){
            ans+=v[dq[st]];
        }
    }
    fprintf(fout, "%lld\n", ans);
    fclose(fin);
    fclose(fout);
    return 0;
}