{"raw_statement":[{"iden":"problem statement","content":"A string $S$ consisting of lowercase English letters is a **good string** if and only if it satisfies the following property for all integers $i$ not less than $1$:\n\n*   There are exactly zero or exactly two different letters that appear exactly $i$ times in $S$.\n\nGiven a string $S$, determine if it is a good string."},{"iden":"constraints","content":"*   $S$ is a string of lowercase English letters with a length between $1$ and $100$, inclusive."},{"iden":"input","content":"The input is given from Standard Input in the following format:\n\n$S$"},{"iden":"sample input 1","content":"commencement"},{"iden":"sample output 1","content":"Yes\n\nFor the string `commencement`, the number of different letters that appear exactly $i$ times is as follows:\n\n*   $i=1$: two letters (`o` and `t`)\n*   $i=2$: two letters (`c` and `n`)\n*   $i=3$: two letters (`e` and `m`)\n*   $i\\geq 4$: zero letters\n\nTherefore, `commencement` satisfies the condition of a good string."},{"iden":"sample input 2","content":"banana"},{"iden":"sample output 2","content":"No\n\nFor the string `banana`, there is only one letter that appears exactly one time, which is `b`, so it does not satisfy the condition of a good string."},{"iden":"sample input 3","content":"ab"},{"iden":"sample output 3","content":"Yes"}],"translated_statement":null,"sample_group":[],"show_order":["default"],"formal_statement":null,"simple_statement":null,"has_page_source":true}