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

int main() {
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr);
    
    int N; cin >> N;
    long long bx = 0,vx = 0,by = 0,vy = 0;
    while(N--){
        long long x,y; cin >> x >> y;
        long long nx = max(vx,vy),ny = max(vx,vy);
        if(x == bx) ny = max(ny,vx+x);
        if(x == by) ny = max(ny,vy+x);
        if(y == bx) nx = max(nx,vx+y);
        if(y == by) nx = max(nx,vy+y);
        if(x == y) nx += x,ny += x;
        bx = x,by = y,vx = nx,vy = ny;
    }
    cout << max(vx,vy) << endl;
}