read N
read A
read B
read C
S=0
for i in `seq 0 $(($N-1))`; do
	a=${A:$i:1}
	b=${B:$i:1}
	c=${C:$i:1}
    if [ $a != $b ] && [ $b != $c ] && [ $a != $c ] ; then
    	S=$(($S+2))
    elif [ $a = $b ] && [ $b = $c ]; then
    	S=$S
    else
    	S=$(($S+1))
    fi
done

echo $S
