#include<bits/stdc++.h>
using namespace std;

#define rep(i,n) for(ll i=0;i<(n);++i)
using ll = long long;
using pll = pair<ll,ll>;
constexpr ll INF = (1LL<<60);
constexpr ll MOD = (1e9+7);
//constexpr ll MOD = (998244353);
template<class T> bool chmax(T &a,const T &b){if(a<b){a=b;return 1;}return 0;}
template<class T> bool chmin(T &a,const T &b){if(a>b){a=b;return 1;}return 0;}
void dump(){cout<<endl;}
template<class T,class... Ts> void dump(T&& h, Ts&&... t){cout<<h<<", ";dump(forward<Ts>(t)...);}
template<class T> istream &operator>>(istream&is,vector<T>&v){for(auto &elemnt:v)is>>elemnt;return is;}
template<class T,class U> istream &operator>>(istream&is,pair<T,U>&p){is>>p.first>>p.second;return is;}
template<class T>vector<T> make_vector(size_t a){return vector<T>(a);}
template<class T, class... Ts>auto make_vector(size_t a, Ts... ts){return vector<decltype(make_vector<T>(ts...))>(a, make_vector<T>(ts...));}

void solve1();void solve2();
int main(){
  solve1();
  return 0;
}

void solve1(){

  ll n;
  cin>>n;
  vector<ll> a(n-1),b(n-1);
  rep(i,n-1)cin>>a[i]>>b[i];

  ll asum = accumulate(a.begin(),a.end(),0);
  ll bsum = accumulate(b.begin(),b.end(),0);

  ll ans = 0;
  rep(a0,bsum+1){
    ll b0 = asum+a0-bsum;
    if(b0<0)continue;
    bool ok = true;
    rep(i,n-1){
      if(a[i]>(bsum+b0)-b[i])ok=false;
    }
    if(ok)ans++;
  }
  cout<<(ans)<<endl;
  

}