Fox and Hedgehog are going up a staircase with a certain number of steps. Fox goes three steps up with each jump (though if necessary, he will just jump the last step). Hedgehog goes seven steps up with each jump (though if necessary, he will just jump the last steps if there are fewer than 7 steps left). Suppose Hedgehog takes 15 fewer jumps than Fox to reach the top of the staircase. Let $s$ denote the sum of all possible numbers of steps this staircase can have. What is the sum of the digits of $s$?