P17640 [ICPC 2019 Yinchuan R] Base62

As we already know, base64 is a common binary-to-text encoding scheme. Here we define a special series of positional systems that represent numbers using a base (a.k.a. radix) of $2$ to $62$. The symbols '$0$' -- '$9$' represent zero to nine, and 'A' -- 'Z' represent ten to thirty-five, and 'a' -- 'z' represent thirty-six to sixty-one. Now you need to convert some integer $z$ in base $x$ into base $y$.

The input contains three integers $x, y~(2 \le x, y \le 62)$ and $z~(0 \le z < x^{120})$, where the integer $z$ is given in base $x$.

Output the integer $z$ in base $y$.