import sequtils,strutils,math

var
    N = stdin.readline.parseInt
    V = stdin.readline.split.map(parseInt)
    dp : array[1002,array[2,int]]

for i,v in V:
    dp[i + 1][0] = max(dp[i])
    dp[i + 1][1] = dp[i][0] + v

echo max(dp[N])