read n
read -d ""

LC_ALL=C
X=0
AB=`echo "${REPLY}" | tac`
B_CHK=`echo "${REPLY}" | awk '{print $2}' | grep -wc 1`

for i in `seq 2 $((n + 1))`
do
        A=`echo "${AB}" | awk -v NUM=$i 'NR==NUM {print $1}'`
        A=$((A + X))
        B=`echo "${AB}" | awk -v NUM=$i 'NR==NUM {print $2}'`

        if [ $A -gt $B ] > /dev/null 2>&1
        then
                X=$(( X + $((B - $((A % B)) )) ))
        elif [ $A -lt $B ] > /dev/null 2>&1
        then
                X=$(( X + $((B - A)) ))
        fi
done
echo $((X - B_CHK))
