#include <iostream>

const int NMAX = 40;
int A[NMAX];
int B[NMAX];

int main() {
  int N;
  std::cin >> N;
  int in = 0;
  int out = 0;
  for (int i = 1; i < N; ++i) {
    std::cin >> A[i] >> B[i];
    in += A[i];
    out += B[i];
  }
  int mi = std::max(0, out - in);
  int ma = std::min(in, out);

  for (int i = 1; i < N; ++i) {
    mi = std::max(mi, B[i] - in + A[i]);
    mi = std::max(mi, A[i] - in);
  }
  std::cout << std::max(0, ma - mi + 1) << std::endl;
}