Untitled

def min_days_to_defeat_elite(your_power, opponent_powers):
    days = 1
    current_power = your_power
    
    for opponent_power in opponent_powers:
        if opponent_power >= your_power:
            return -1
        
        if current_power <= opponent_power:
            days += 1
            current_power = your_power
        
        current_power -= opponent_power
    
    return days

your_power = int(input().strip())
n = int(input().strip())
opponent_powers = list(map(int, input().strip().split()))

result = min_days_to_defeat_elite(your_power, opponent_powers)
print(result)