Three squares $ABCD$, $CDEF$, and $FGHI$ are equal in area, each with side length $s$. They are arranged such that square $ABCD$ is to the left of square $CDEF$, and square $FGHI$ is above square $CDEF$. Point $M$ is the midpoint of side $AD$ of square $ABCD$, and point $N$ is the midpoint of side $HI$ of square $FGHI$. What is the ratio of the area of the shaded quadrilateral $MNCG$ to the sum of the areas of the three squares?