https://www.acmicpc.net/problem/2455
const fs=require('fs')
let ip=fs.readFileSync('/dev/stdin').toString().split('\n')
sum=0
max=0
for(i=0;i<4;i++){
v=ip[i].split(' ')
a=parseInt(v[0])
b=parseInt(v[1])
sum+=-a+b
if(sum>=max) max=sum
}
console.log(max)