Minimum of the tilted double well $\frac\lambda4(x^2-v^2)^2-\epsilon x$ for small $\epsilon$

Find the minimal value of the function \(f ( x ) = \frac { \lambda } { 4 } ( x ^ { 2 } - v ^ { 2 } ) ^ { 2 } - \epsilon x , \lambda , \epsilon > 0\) , to the leading order in \(\epsilon \ll 1\)