#include <stdio.h>
int main() {
int n, m, i, j, k, a[100001], sum = 0;
long long min = 100000;
scanf("%d%d", &n, &m);
for (i = 0; i < n; i++)
scanf("%d", &a[i]);
for (i = 0; i < n - m; i++) {
sum = 0;
for (j = i; j < i + m; j++) {
sum = sum + a[j];
}
if (sum < min)
min = sum;
}
printf("%d", min);
return 0;
}