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

unsigned long long a[1000005];
unsigned long long b[1000005];
unsigned long long c[1000005];
unsigned long long n, k, l, sum;

//void sort(unsigned long long * b, unsigned long long len);
int main()
{
	int i, j;
	scanf("%lu%lu", &n, &k);
	for (i=0; i<n-1; i++) 
		scanf("%lu", &a[i]);
		
	c[0] = a[0];
	for (i=0; i<n-1; ++i) {
		c[i+1] = c[i] + a[i+1];
	}
	
	for (i=0; i<n-k; ++i) {
		for (j=i; j<k+i; ++j) 
		    l += a[j]; 
		    
			   //b[i] = l;
		       
		       if (l>sum)
		         sum = l;
		         l = 0;
		   }
			
			
					
		//b[i] = l;
		//l = 0;
	   
	//sort(b, n-k);

	
	printf("%lu\n", c[n-2]-sum);
		
    return 0;	
   
}
/*
void sort(unsigned long long * b, unsigned long long len)
{
      unsigned long long i, j, t;
      for (i=0; i<len-1; i++) {
      	for (j=0; j<len-1-i; ++j) {
      		if (b[j] < b[j+1]) {
      			t = b[j];
      			b[j] = b[j+1];
      			b[j+1] = t;
			  }
		  }
	  }
}
*/