fence.cpp

#include <bits/stdc++.h>

using namespace std;

int main() {
  int n, k;
  cin >> n >> k;

  vector<int> h(n);
  for (int i = 0; i < n; ++i) {
    cin >> h[i];
  }

  // Calculate initial sum
  int sum = 0;
  for (int i = 0; i < k; ++i) {
    sum += h[i];
  }

  int smallest = 1000000000;
  int smallestPos;
  for (int i = 0; i + k <= n; ++i) {
    // Is the the best place we'e seen so far?
    if (sum < smallest) {
      smallest = sum;
      smallestPos = i;
    }

    // Slide the window 1 plank to the right, unless we're at the end
    if (i + k < n) {
      sum -= h[i];
      sum += h[i + k];
    }
  }

  cout << smallestPos + 1 << endl;

  return 0;
}