#include <bits/stdc++.h>
#include <cstdlib>
#include <math.h>
using namespace std;

using ll = long long;


int main(){
    int n;
    cin >> n;
    vector<ll>x(n),y(n);
    ll s=0;
    for(int i=0;i<n;i++){
        cin >> x[i] >> y[i];
        if(x[i]==y[i])s+=x[i];
    }
    vector dp(n,vector<ll>(2,s));
    for(int i=1;i<n;i++){
        dp[i][0]=
        max(
            dp[i-1][0]+(y[i-1]==x[i])*x[i],
            dp[i-1][1]+(x[i-1]==x[i])*x[i]
        );
        dp[i][1]=
        max(
            dp[i-1][0]+(y[i-1]==y[i])*y[i],
            dp[i-1][1]+(x[i-1]==y[i])*y[i]
        );
    }
    cout << max(dp[n-1][0],dp[n-1][1]) << endl;
    return 0;
}