#include <bits/stdc++.h>
#define REP(i, n) for (int i = 0; (i) < (int)(n); ++ (i))
#define REP3(i, m, n) for (int i = (m); (i) < (int)(n); ++ (i))
#define REP_R(i, n) for (int i = (int)(n) - 1; (i) >= 0; -- (i))
#define REP3R(i, m, n) for (int i = (int)(n) - 1; (i) >= (int)(m); -- (i))
#define ALL(x) std::begin(x), std::end(x)
using namespace std;

typedef long long ll;
constexpr int INF = 1e9 + 7;
class max_flow {
    struct edge_t {
        int to;
        ll cap;
        int rev;
    };
    int v;
    vector<vector<edge_t> > g;
    vector<int> iter, level;
public:
    max_flow(int v_)
            : v(v_), g(v) {
    }
    void add_edge(int from, int to, ll cap) {
        g[from].push_back((edge_t) { to, cap, (int)g[to].size() });
        g[to].push_back((edge_t) { from, 0ll, (int)g[from].size() - 1 });
    }
private:
    void bfs(int src) {
        level.assign(v, -1);
        queue<int> q;
        level[src] = 0;
        q.push(src);
        while (not q.empty()) {
            int x = q.front();
            q.pop();
            for (auto & e : g[x]) {
                if (e.cap > 0 and level[e.to] < 0) {
                    level[e.to] = level[x] + 1;
                    q.push(e.to);
                }
            }
        }
    }
    ll dfs(int x, int dst, ll flow) {
        if (x == dst) return flow;
        for (int & i = iter[x]; i < (int)g[x].size(); ++ i) {
            edge_t & e = g[x][i];
            if (e.cap > 0 and level[x] < level[e.to]) {
                ll d = dfs(e.to, dst, min(flow, e.cap));
                if (d > 0) {
                    e.cap -= d;
                    g[e.to][e.rev].cap += d;
                    return d;
                }
            }
        }
        return 0;
    }
public:
    ll run_destructive(int src, int dst) {
        ll flow = 0;
        bfs(src);
        while (level[dst] >= 0) {
            iter.assign(v, 0);
            while (true) {
                ll delta = dfs(src, dst, INF);
                if (delta <= 0) break;
                flow += delta;
            }
            bfs(src);
        }
        return flow;
    }
};


int solve(int n, vector<int> a, vector<int> b) {
    int sum_a = accumulate(ALL(a), 0);
    int sum_b = accumulate(ALL(b), 0);
    if (sum_a > sum_b) {
        a.swap(b);
        swap(sum_a, sum_b);
    }
    max_flow g(2 * n);
    const int src = n - 1;
    const int dst = 2 * n - 1;
    REP (i, n - 1) {
        g.add_edge(src, i, a[i]);
        REP (j, n - 1) if (j != i) {
            g.add_edge(i, n + j, min(a[i], b[j]));
        }
        g.add_edge(n + i, dst, b[i]);
    }
    int l = sum_b - g.run_destructive(src, dst);
    int r = sum_b;
    return r - l + 1;
}

int main() {
    int n; cin >> n;
    vector<int> a(n - 1), b(n - 1);
    REP (i, n - 1) {
        cin >> a[i] >> b[i];
    }
    cout << solve(n, a, b) << endl;
    return 0;
}