#include <bits/stdc++.h>
using namespace std;
const long long N = 1e5 + 5;
void pairsort(long long a[], long long b[], long long n) {
  pair<long long, long long> pairt[n];
  for (long long i = 0; i < n; i++) {
    pairt[i].first = a[i];
    pairt[i].second = b[i];
  }
  sort(pairt, pairt + n);
  for (long long i = 0; i < n; i++) {
    a[i] = pairt[i].first;
    b[i] = pairt[i].second;
  }
}
long long gcd(long long a, long long b) {
  if (b == 0) return a;
  return gcd(b, a % b);
}
long long isPrime(long long n) {
  if (n < 2) return 0;
  if (n < 4) return 1;
  if (n % 2 == 0 or n % 3 == 0) return 0;
  for (long long i = 5; i * i <= n; i += 6)
    if (n % i == 0 or n % (i + 2) == 0) return 0;
  return 1;
}
long long C(long long n, long long r) {
  if (r > n - r) r = n - r;
  long long ans = 1;
  for (long long i = 1; i <= r; i++) {
    ans *= n - r + i;
    ans /= i;
  }
  return ans;
}
long long mod = 1e9 + 7;
long long modexpo(long long x, long long p) {
  long long res = 1;
  x = x % mod;
  while (p) {
    if (p % 2) res = res * x;
    p >>= 1;
    x = x * x % mod;
    res %= mod;
  }
  return res;
}
long long H, n, a[200005], b[200005], m, s, r, ans, ans1, H1;
int32_t main() {
  ios::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  ;
  cin >> H >> n;
  for (long long i = 0; i < n; i++) cin >> a[i], s += a[i];
  b[0] = a[0];
  m = a[0];
  for (long long i = 1; i < n; i++) {
    b[i] = b[i - 1] + a[i];
    m = (m < b[i] ? m : b[i]);
  }
  H1 = H;
  for (long long i = 0; i < n && H1 > 0; i++) {
    ans1++;
    H1 += a[i];
    if (H1 <= 0) {
      cout << ans1;
      return 0;
    }
  }
  if (s >= 0) {
    cout << -1;
    return 0;
  }
  s = -s;
  r = (0 > (H + m) / s - 1 ? 0 : (H + m) / s - 1);
  H -= r * s;
  ans = r * n;
  for (long long i = 0; i < n && H > 0; i++) {
    ans++;
    H += a[i];
    if (H <= 0) break;
  }
  for (long long i = 0; i < n && H > 0; i++) {
    ans++;
    H += a[i];
    if (H <= 0) break;
  }
  for (long long i = 0; i < n && H > 0; i++) {
    ans++;
    H += a[i];
    if (H <= 0) break;
  }
  cout << ans;
  return 0;
}
