2022 4 1贪心好难啊
n=int(input())
f=[]
for i in range(n):
a,b=map(int,input().split())
c=a+b
f.append([c,a,b])
f.sort()
f=[0]+f
s=[0]*50005
for i in range(1,len(f)):
s[i]=s[i-1]+f[i][1]
ans=-1000000005
for i in range(1,n+1):
ans=max(ans,s[i-1]-f[i][2])
if n==1:
print(-f[1][2])
else:
print(ans)