import std;

void main() {
    int N;
    readf("%d\n", N);

    auto p = new long[](N), a = new long[](N);
    foreach (i; 0 .. N) {
        readf("%d %d\n", p[i], a[i]);
    }

    auto dp = new long[](N+1);
    foreach (i; 0 .. N) {
        dp[i+1] = dp[i] + p[i];
        if (i > 0) dp[i+1] = max(dp[i+1], dp[i-1]+a[i-1]+p[i]*2);
    }

    dp[N].writeln;
}