#include <bits/stdc++.h>
using namespace ::std;
const long double PI = acos(-1);
const long long MOD = 1000000000 + 7;
long long gcd(long long a, long long b) { return b == 0 ? a : gcd(b, a % b); }
long long add(long long a, long long b, long long m = MOD) {
  if (a >= m) a %= m;
  if (b >= m) b %= m;
  if (a < 0) a += m;
  if (b < 0) b += m;
  long long res = a + b;
  if (res >= m or res <= -m) res %= m;
  if (res < 0) res += m;
  return res;
}
long long mul(long long a, long long b, long long m = MOD) {
  if (a >= m) a %= m;
  if (b >= m) b %= m;
  if (a < 0) a += m;
  if (b < 0) b += m;
  long long res = a * b;
  if (res >= m or res <= -m) res %= m;
  if (res < 0) res += m;
  return res;
}
long long pow_mod(long long a, long long b, long long m = MOD) {
  long long res = 1LL;
  a = a % m;
  while (b) {
    if (b & 1) res = mul(res, a, m);
    b >>= 1;
    a = mul(a, a, m);
  }
  return res;
}
long long fastexp(long long a, long long b) {
  long long res = 1LL;
  while (b) {
    if (b & 1) res = res * a;
    b >>= 1;
    a *= a;
  }
  return res;
}
int gcdExtendido(int a, int b, int *x, int *y) {
  if (a == 0) {
    *x = 0;
    *y = 1;
    return b;
  }
  int x1, y1;
  int gcd = gcdExtendido(b % a, a, &x1, &y1);
  *x = y1 - (b / a) * x1;
  *y = x1;
  return gcd;
}
int modInverso(int a, int m) {
  int x, y;
  int g = gcdExtendido(a, m, &x, &y);
  if (g != 1)
    return -1;
  else
    return (x % m + m) % m;
}
const int N = 200000 + 5;
int n;
long long H;
long long d[N];
int main() {
  scanf("%lld", &(H));
  scanf("%d", &(n));
  long long S = 0;
  for (int i = 1; i <= n; i++) {
    scanf("%lld", &(d[i]));
    S += d[i];
    d[i] += d[i - 1];
  }
  long long ans = LLONG_MAX;
  for (int i = 1; i <= n; i++) {
    long long tail = d[i];
    long long L = tail + H;
    long long R = S;
    if (L <= 0) {
      ans = min(ans, 1LL * i);
      continue;
    }
    if (R >= 0) continue;
    L = abs(L);
    R = abs(R);
    long long act = 1LL * i + 1LL * n * ((L + R - 1) / R);
    ans = min(ans, act);
  }
  if (ans == LLONG_MAX)
    puts("-1");
  else
    cout << ans << endl;
  return 0;
}
