#include <iostream>
#include <algorithm>
#include <cmath>
using namespace std;

int a[300010];

int main()
{
    int n, m;
    cin >> n >> m;
    int l = 0, r = 0;
    int ans = 0, heat = 0x3f3f3f;
    while (r < n)
    {
        cin >> a[r];
        if (r < m)
            ans += a[r ++];
        else 
        {
            ans += a[r ++];
            ans -= a[l ++];
            heat = min(ans, heat);
        }
    }
    heat = min(ans, heat);
    cout << heat;
    return 0;
}