import sys
input = sys.stdin.readline

N = int(input())
dp = [[0]*2 for _ in range(N+1)]
dp[0][1] = -10**18

for i in range(N):
    p, a = map(int, input().split())
    dp[i+1][0] = max(dp[i][0]+p, dp[i][1]+2*p)
    dp[i+1][1] = max(dp[i][0]+a, dp[i][1]+2*a)

print(max(dp[N]))