编写一个程序,输入一个字符串统计字符串中字母、数字及其他字符的个数。
```python
s = input("输入一个字符串：")
letter_count = 0
digit_count = 0
other_count = 0
for char in s:
if char.isalpha():
letter_count += 1
elif char.isdigit():
digit_count += 1
else:
other_count += 1
print("字母个数：", letter_count)
print("数字个数：", digit_count)
print("其他字符个数：", other_count)
```