Input (grade 8): Several times, he withdrew from public performances - during 1936 to 1938, 1953 to 1965, 1969 to 1974, and 1983 to 1985.
Output (grade 11): Horowitz stopped playing concerts four times (1936 to 1938, 1953 to 1965, 1969 to 1974, and 1983 to 1985), as he was unsure that he was good enough, even when he was popular.