use proconio::input;

fn main() {
    input! {
        n: usize,
        xy: [[usize; 2]; n],
    }

    let init_score = if xy[0][0] == xy[0][1] { xy[0][0] } else { 0 };
    let mut dp = [init_score; 2];
    for window in xy.windows(2) {
        let mut next_dp = [0_usize; 2];
        for from in 0..2 {
            for to in 0..2 {
                let add_score_1 = if window[0][1 - from] == window[1][to] {
                    window[1][to]
                } else {
                    0
                };
                let add_score_2 = if window[1][0] == window[1][1] {
                    window[1][0]
                } else {
                    0
                };
                next_dp[to] = next_dp[to].max(dp[from] + add_score_1 + add_score_2);
            }
        }
        dp = next_dp;
    }

    let max_score = dp[0].max(dp[1]);
    println!("{max_score}");
}