#include <bits/stdc++.h>
#include <atcoder/all>

using namespace std;
using namespace atcoder;
typedef long long ll;
#define rep(i, n) for (ll i = 0; i < (ll)(n); i++)
static const double pi = 3.141592653589793;
const ll INF = 1LL << 60;
const ll mod = 1000000007;
const ll imod = 998244353;
using mint = modint998244353;
vector<int> dx = {1, 0, -1, 0}, dy = {0, 1, 0, -1};
ll P(ll x, ll n) {
  ll ret = 1;
    while (n > 0) {
      if (n & 1) ret *= x;
      x *= x;
      n >>= 1;
  }
  return ret;
}

void seek(bool f){
  cout << (f ? "Yes" : "No") << endl;
}

int main(){
	ll N;
	cin >> N;
	vector<ll> A(N), B(N);
	rep(i, N){
		cin >> A[i] >> B[i];
	}
	ll dp[N + 1][2];
	rep(i, N + 1){
		rep(j, 2){
			dp[i][j] = 0;
		}
	}
	if(A[0] == B[0]){
		dp[0][0] = dp[0][1] = A[0];
	}
	for(int i = 0; i < N; i++){
		dp[i + 1][0] = max(dp[i][0], dp[i][1]);
		dp[i + 1][1] = max(dp[i][0], dp[i][1]);
		if(i < N - 1 and A[i + 1] == A[i]){
			dp[i + 1][0] = max(dp[i + 1][0], dp[i][1] + A[i]);
		}
		if(i < N - 1 and A[i + 1] == B[i]){
			dp[i + 1][0] = max(dp[i + 1][0], dp[i][0] + B[i]);
		}
		if(i < N - 1 and B[i + 1] == A[i]){
			dp[i + 1][1] = max(dp[i + 1][1], dp[i][1] + A[i]);
		}
		if(i < N - 1 and B[i + 1] == B[i]){
			dp[i + 1][1] = max(dp[i + 1][1], dp[i][0] + B[i]);
		}
		if(A[i] == B[i]){
			dp[i + 1][0] += A[i];
			dp[i + 1][1] += A[i];
		}
	}
	cout << max(dp[N][0], dp[N][1]) << endl;
}