#include <algorithm>
#include <deque>
#include <iomanip>
#include <iostream>
#include <map>
#include <numeric>
#include <queue>
#include <set>
#include <string>
#include <unordered_map>
#include <unordered_set>
#include <vector>

#define all(v) (v).begin(), (v).end()
#define rep(i, j) for (ll i = 0; i < j; ++i)
#define rep2(i, j, k) for (ll i = j; i <= k; ++i)
#define rep3(i, j, k) for (ll i = j; i >= k; --i)

using namespace std;

using ld = long double;
using ll = long long;
using pi = pair<int,int>;
using pl = pair<ll,ll>;
using vi = vector<int>;
using vl = vector<ll>;
using vpi = vector<pi>;
using vpl = vector<pl>;
using vvi = vector<vi>;
using vvl = vector<vl>;
using vvpi = vector<vpi>;
using vvpl = vector<vpl>;

template <class T> using pqg = priority_queue<T, vector<T>, greater<T>>;
template <class S, class T> inline bool chmax(S& x, T y) { if (x < y) { x = y; return 1; } return 0; }
template <class S, class T> inline bool chmin(S& x, T y) { if (x > y) { x = y; return 1; } return 0; }

constexpr int INF = 1000000000;
constexpr int MAX = 50005;
constexpr int MOD = 1000000007;
constexpr ll INFLL = 1000000000000000000;

int main(void) {
    int n;
    cin >> n;

    vpi in(n-1), out(n-1);
    int inSum = 0, outSum = 0;

    rep(i, n-1) {
        cin >> in[i].first >> out[i].first;
        in[i].second = out[i].second = i;

        inSum += in[i].first;
        outSum += out[i].first;
    }

    sort(all(out), greater<pi>());
    sort(all(in));

    int inRemain = 0, outRemain = 0;

    rep(i, n-1) {
        rep(j, n-1) {
            if (in[i].second == out[j].second) continue;

            int mn = min(in[i].first, out[j].first);
            in[i].first -= mn;
            out[j].first -= mn;
        }

        inRemain += in[i].first;
    }

    rep(i, n-1) outRemain += out[i].first;
    printf("%d\n", outSum - outRemain + 1);

    return (0);
}