{"problem":{"name":"Change Usernames","description":{"content":"You run a web service with $N$ users. The $i$\\-th user with a current handle $S_i$ wants to change it to $T_i$.   Here, $S_1,\\ldots$, and $S_N$ are pairwise distinct, and so are $T_1,\\ldots$, and $T_N","description_type":"Markdown"},"platform":"AtCoder","limit":{"time_limit":2000,"memory_limit":262144},"difficulty":"None","is_remote":true,"is_sync":true,"sync_url":null,"sign":"abc285_d"},"statements":[{"statement_type":"Markdown","content":"You run a web service with $N$ users.\nThe $i$\\-th user with a current handle $S_i$ wants to change it to $T_i$.  \nHere, $S_1,\\ldots$, and $S_N$ are pairwise distinct, and so are $T_1,\\ldots$, and $T_N$.\nDetermine if there is an appropriate order to change their handles to fulfill all of their requests subject to the following conditions:\n\n*   you change only one user's handle at a time;\n*   you change each user's handle only once;\n*   when changing the handle, the new handle should not be used by other users at that point.\n\n## Constraints\n\n*   $1 \\leq N \\leq 10^5$\n*   $S_i$ and $T_i$ are strings of length between $1$ and $8$ (inclusive) consisting of lowercase English letters.\n*   $S_i \\neq T_i$\n*   $S_i$ are pairwise distinct.\n*   $T_i$ are pairwise distinct.\n\n## Input\n\nThe input is given from Standard Input in the following format:\n\n$N$\n$S_1$ $T_1$\n$S_2$ $T_2$\n$\\vdots$\n$S_N$ $T_N$\n\n[samples]","is_translate":false,"language":"English"}],"meta":{"iden":"abc285_d","tags":[],"sample_group":[["2\nb m\nm d","Yes\n\nThe $1$\\-st user with a current handle `b` wants to change it to `m`.  \nThe $2$\\-nd user with a current handle `m` wants to change it to `d`.\nFirst, you change the $2$\\-nd user's handle from `m` to `d`; then you change the $1$\\-st user's handle from `b` to `m`. This way, you can achieve the objective.\nNote that you cannot change the $1$\\-st user's handle to `m` at first, because it is used by the $2$\\-nd user at that point."],["3\na b\nb c\nc a","No\n\nThe $1$\\-st user with a current handle `a` wants to change it to `b`.  \nThe $2$\\-nd user with a current handle `b` wants to change it to `c`.  \nThe $3$\\-rd user with a current handle `c` wants to change it to `a`.\nWe cannot change their handles subject to the conditions."],["5\naaa bbb\nyyy zzz\nccc ddd\nxxx yyy\nbbb ccc","Yes"]],"created_at":"2026-03-03 11:01:13"}}