Chef in Heaven

When Chef was born, his parents took him to the famous monk Doctor Strange to know whether he will land himself in heaven after his life or not. According to Strange, Chef will live for $L$ years in total. If he wants to go to heaven, he must spend at least $50\%$ of his life years doing good deeds. He also shows them his future using a string $S$ of length $L$ where $S_i = 0$ means the $i$-th yea