If each pair of the equation ${\mathrm{x}}^2+\mathrm{ax}+\mathrm{b}=0,{\mathrm{x}}^2+\mathrm{bx}+\mathrm{c}=0\text{ and }{\mathrm{x}}^2+\mathrm{cx}+\mathrm{a}=0$ has a common root, then product of all common roots is