Wallet Bid: Conditional Expected Total

$n$ people each have an amount of money in their wallets, where each amount is independently drawn from $U(0,1)$. The person with the most money wins everyone's money. You are person 1. You see $\$x_1$ in your wallet and are told that you won (i.e., your amount was the largest). What is your estimate of the total amount of money across all $n$ wallets? More precisely, find: $E\left[\sum_{i=1}^n X_i \;\middle|\; X_1 = x_1,\; X_1 = \max(X_1, \ldots, X_n)\right]$ Report the numerical answer when $x_1 = 0.75$ and $n = 15$.