Snuke 嘅字典入面有 $n$ 個唔同嘅字 $s_1, \ldots, s_n$。每個字都由英文小寫字母組成。呢啲字按字典序排列，即係 $s_1 < \cdots < s_n$。可惜，你睇唔清字典入面一啲字元，於是將呢啲字元換成咗「?」。請計算有幾多種方法，可以將每個「?」換成一個英文小寫字母，令本字典有效，答案對 $1\,000\,000\,007$ 取模。
輸入第一行有一個整數 $n$（$1 \le n \le 50$）。之後有 $n$ 行，第 $i$ 行有個字 $s_i$（$1 \le |s_i| \le 20$，$s_i$ 入面每個字元都係英文小寫字母或者「?」）。
輸出答案。
2 ?sum??mer c??a??mp
703286064
3 snuje ????e snule
1
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