已知平面向量\( \overrightarrow {a}\)，\( \overrightarrow {b}\)，\( \overrightarrow {c}\)，\( \overrightarrow {d}\)满足\(| \overrightarrow {a} |=| \overrightarrow {b} |=| \overrightarrow {c} |=1\)，\( \overrightarrow {a} ⋅ \overrightarrow {c} = \overrightarrow {b} ⋅ \overrightarrow {c} = \dfrac {1- \overrightarrow {a}\cdot \overrightarrow {b}}{ \overrightarrow {a}\cdot \overrightarrow {d}} > 0\)，\( \overrightarrow {c} ⋅ \overrightarrow {d} =0\)，若平面向量\( \overrightarrow {s} =x \overrightarrow {a} +y \overrightarrow {b} (x , y > 0\)且\(xy=1)\)，则\(| \overrightarrow {s} +2 \overrightarrow {c} |+| \overrightarrow {s} - \overrightarrow {d} |\)的最小值是______．