#include using namespace std; typedef long long ll; typedef pair pii; typedef pair pll; #define pb push_back #define mp make_pair #define rep(i,n) for(int i=0;i<(n);++i) constexpr int mod=1000000007; constexpr int mod1=998244353; vector dx={0,1,0,-1},dy={-1,0,1,0}; bool inside(int y,int x,int h,int w){ if(y=0 && x=0) return true; return false; } int main(){ cin.tie(0); ios::sync_with_stdio(false); int n;cin >> n; n--; vector a(n), b(n); int sum1 = 0, sum2 = 0; rep(i,n){ cin >> a.at(i) >> b.at(i); sum1 += a.at(i); sum2 += b.at(i); } ll ans = 0; rep(i,1000000){ bool ok = true; int b1 = sum1 + i - sum2; if(b1 < 0 || i > sum2) continue; rep(j,n){ if(a.at(j) > sum2 + b1 - b.at(j)) ok = false; } if(ok) ans++; } cout << ans << endl; }