#include <bits/stdc++.h>

using namespace std;

typedef pair<int, int> pii;
typedef long long ll;
const int N = 2000086, MOD = 998244353, INF = 0x3f3f3f3f;
int n, m, w[N];

int x[N], y[N];
ll f[N][2];
int main() {
    cin >> n;
    for (int i = 1; i < n + 1; i++) {
        scanf("%d%d", x + i, y + i);
        f[i][0] = max(f[i - 1][0] + (x[i] == y[i - 1]) * x[i], f[i - 1][1] + (x[i] == x[i - 1]) * x[i]) + (x[i] == y[i]) * x[i];
        f[i][1] = max(f[i - 1][0] + (y[i] == y[i - 1]) * y[i], f[i - 1][1] + (y[i] == x[i - 1]) * y[i]) + (x[i] == y[i]) * x[i];
    }
    printf("%lld\n", max(f[n][0], f[n][1]));
    return 0;
}