#include <cstdio>
#include <climits>
#include <iostream>
#include <algorithm>
#include <string>
#include <cstdio>
#include <climits>
#include <iostream>
#include <algorithm>
#include <string>
#include <vector>
#include <utility>
#include <queue>
#include <cstring>
#define rep(i, n) for (int i = 0; i < (n); i++)
using namespace std;
const long long MOD = 1000000007;

typedef long long ll;

int
main(int argc, char *argv[])
{
  int n; cin >> n;
  int a[50], b[50];
  int in = 0, out = 0;
  rep(i, n - 1) {
    cin >> a[i + 1] >> b[i + 1];
    in += a[i + 1]; out += b[i + 1];
  }
  if (in < out) {
    int tmp;
    tmp = in; in = out; out = tmp;
    rep(i, n) {
      tmp = a[i];
      a[i] = b[i]; b[i] = tmp;
    }
  }
 
    int l = -1, r = out;
    while (r - l > 1) {
      int med = (l + r) / 2;
      a[0] = med; b[0] = in - out + med;
      bool flag = true;
      rep(i, n) {
	if (a[i] > in + med - b[i]) {
	  flag = false;
	  break;
	}
	if (b[i] > in + med - a[i]) {
	  flag = false;
	  break;
	}
      }
      if (flag) r = med;
      else l = med;
    }
    cout << out - r + 1 << endl;
  
  return 0;
}