import java.util.*;

public class Main {
  public static void main(String[] args) {
    Scanner cin = new Scanner(System.in);
    long h = cin.nextLong(), tar, sum = 0, MIN = 0;
    int n = cin.nextInt();
    int[] v = new int[n];
    for (int i = 0; i < n; i++) {
      v[i] = cin.nextInt();
      sum += v[i];
      if (h + sum <= 0) {
        System.out.println(i + 1);
        cin.close();
        return;
      }
      MIN = Math.min(MIN, sum);
    }
    if (sum >= 0) {
      System.out.println(-1);
      cin.close();
      return;
    }
    tar = ((h + MIN) / (-sum) - 1) * n;
    h += tar / n * sum;
    for (int i = 0; h > 0; ++i) {
      tar += 1;
      h += v[i];
      if (i + 1 == n) {
        i = -1;
      }
    }
    System.out.println(tar);
    cin.close();
  }
}

/*
 * ###################################################################
 * #.................................................................#
 * #.............#......#............Created.By.RBTree...............#
 * #............#.#....#.#........... Limiting-Factor................#
 * #.............########............................................#
 * #............#........#..##############################...........#
 * #...........#..V....V......#..#........................#..#...#...#
 * #............#........#....#..........###..###..........#..#.#.#..#
 * #............#..X##X..#..#............#....#.#...........#..#...#.#
 * #...........#...N##N...#..#...........###..###..........#.........#
 * #.......MOO..#..@.....#....#.#.#.#...................#.#..........#
 * #.............########.....#.#.#.##############.#.#..#.#..........#
 * #..........................#.#.#.#.............#.#.#.#.#..........#
 * #......#########...........#.#.#.#.................#.#.#..........#
 * #.....#.........#..........#.#.#.#.................#.#.#..........#
 * #.#.#.#G#R#A#S#S#.#.#......#.#.#.#.................#.#.#..........#
 * #.###################......#.#.#.#.................#.#.#..........#
 * #...........................#.#.#...................#.#...........#
 * #.................................................................#
 * ###################################################################
 */