https://www.acmicpc.net/problem/10833
const fs=require('fs')
ip=fs.readFileSync(0).toString().split('\n')
n=parseInt(ip[0])
sum=0
for(i=1;i<=n;i++){
v=ip[i].split(' ').map(Number)
a=parseInt(v[0])
b=parseInt(v[1])
sum+=b%a
}
console.log(sum)