#include "bits/stdc++.h"
using namespace std;
#ifdef _DEBUG
#include "dump.hpp"
#else
#define dump(...)
#endif

#define int long long
#define rep(i, a, b) for (int i = (a); i < (b); i++)
#define rrep(i, a, b) for (int i = (b)-1; i >= (a); i--)
#define all(c) begin(c), end(c)
const int INF =
    sizeof(int) == sizeof(long long) ? 0x3f3f3f3f3f3f3f3fLL : 0x3f3f3f3f;
const int MOD = 1e9 + 7;
template <class T>
bool chmax(T &a, const T &b) {
    if (a < b) {
        a = b;
        return true;
    }
    return false;
}
template <class T>
bool chmin(T &a, const T &b) {
    if (b < a) {
        a = b;
        return true;
    }
    return false;
}

signed main() {
    cin.tie(0);
    ios::sync_with_stdio(false);
    int N;
    cin >> N;
    vector<int> A(N), B(N);
    rep(i, 1, N) { cin >> A[i] >> B[i]; }

    int cnt = 0;
    rep(i, 0, 370010) {
        A[0] = i;
        B[0] = 0;
        int IN = 0, OUT = 0;
        rep(j, 0, N) {
            IN += A[j];
            OUT += B[j];
        }
        B[0] = IN - OUT;
        OUT += B[0];
        if (B[0] < 0) continue;
        bool ok = true;
        rep(j, 0, N) {
            if (A[j] > OUT - B[j]) ok = false;
            if (IN - A[j] < B[j]) ok = false;
        }
        if (ok) { cnt++; }
    }
    cout << cnt << endl;

    return 0;
}