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

long long v[100000],a[10000];

long i,j,min,k,x,n,s;


int main (){
 FILE * f = fopen("deque.in","r");
 FILE * g = fopen("deque.out","w");

 fscanf(f,"%ld",&n);
 fscanf(f,"%ld",&k);

 for(i=1;i<=n;i++)
	fscanf(f,"%lld",&v[i]);


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

	min=10000;

	for(j=i;j<i+k;j++)

		if(min>v[j])
			min=v[j];
	a[++x]=min;
	}

 s=0;
 for(i=1;i<=x;i++)
	s+=a[i];

 fprintf(g,"%ld",s);


 fclose(f);
 fclose(g);

return 0;
}