14．已知函数 $f(x)=\sin x$ ．若存在 $x_{1}, x_{2}, \ldots, x_{m}$ 满足 $0 \leq x_{1}<x_{2}<\cdots<x_{m} \leq 6 \pi$ ，且 $\left|f\left(x_{1}\right)-f\left(x_{2}\right)\right|+\left|f\left(x_{2}\right)-f\left(x_{3}\right)\right|+\cdots+\left|f\left(x_{m-1}\right)-f\left(x_{m}\right)\right|=12\left(m \geq 2, m \in \mathbf{N}^{*}\right)$ ，则 $m$的最小值为
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