#include<cstdio>
int n,k,i,j,p,u,d[5000001],v[5000001];
long long s;
FILE *f,*g;
int main(){
    f=fopen("deque.in","r");
    g=fopen("deque.out","w");
    fscanf(f,"%d%d",&n,&k);
    p=1;
    u=0;
    for(i=1;i<=n;i++){
        fscanf(f,"%d",&v[i]);
    }
    for(i=1;i<=n;i++){
        while(v[i]<v[d[u]] && u>=p){
            u--;
        }
        d[++u]=i;
        if(i>=k){
            if(i-d[p]==k)
                p++;
            s+=v[d[p]];
        }
    }
    fprintf(g,"%lld",s);
    fclose(f);
    fclose(g);
    return 0;
}