SE-SKOLORNAS 1993 Problem 2

A railway line is divided into ten sections by the stations $A,B,C,D,E,F, G,H,I,J,K$ . The length of each section is an integer number of kilometers and the distacne between $A$ and $K$ is $56$ km. A trip along two successive sections never exceeds $12$ km, but a trip along three successive sections is at least $17$ km. What is the distance between $B$ and $G$ ?