#include <bits/stdc++.h>
 
using namespace std;
 
typedef long long ll;
typedef pair<ll,ll> P;
 
long long int INF = 1e18;
double Pi = 3.1415926535897932384626;
 
//vector<ll> G[500005];
//vector<P> tree[500010];
priority_queue <ll> pql;
priority_queue <P> pqp;
//big priority queue
priority_queue <ll,vector<ll>,greater<ll> > pqls;
priority_queue <P,vector<P>,greater<P> > pqps;
//small priority queue
//top pop
 
int dx[8]={1,0,-1,0,1,1,-1,-1};
int dy[8]={0,1,0,-1,1,-1,-1,1};
char dir[] = "DRUL";
//ll bit[500005];
//↓,→,↑,←
 
 
#define p(x) cout<<x<<endl;
#define el cout<<endl;
#define pe(x) cout<<(x)<<" ";
#define ps(x) cout<<fixed<<setprecision(25)<<x<<endl;
#define pu(x) cout<<(x);
#define pb push_back
#define lb lower_bound
#define ub upper_bound
#define CLEAR(a) a = decltype(a)(); 
 
 
ll mod = 998244353;
ll rui(ll number1,ll number2){
 
    if(number2 == 0){
        return 1;
    }else{
        ll number3 = rui(number1,number2 / 2);
        number3 *= number3;
        number3 %= mod;
        if(number2%2==1){
            number3 *= number1;
            number3 %= mod;
        }
        return number3;
    }
}
ll gcd(ll number1,ll number2){
 
    if(number1 > number2){
        swap(number1,number2);
    }
    if(number1 == 0 || number1 == number2){
        return number2;
    }else{
        return gcd(number2 % number1,number1);
    }
}
void YES(bool condition){
 
    if(condition){
        p("YES");
    }else{
        p("NO");
    }
    return;
}
void Yes(bool condition){
 
    if(condition){
        p("Yes");
    }else{
        p("No");
    }
    return;
}
 
//ll fact[800005],rfact[800005];
/*
void c3_init(){
    fact[0] = rfact[0] = 1;
    for(ll i=1; i<=800000; i++){
        fact[i] = (fact[i-1]*i) % mod;
    }
    rfact[800000] = rui(fact[800000],mod - 2);
    for(ll i=800000; i>=1; i--){
       rfact[i-1] = rfact[i] * i;
       rfact[i-1] %= mod;
    }
    return;}
ll c3(ll n,ll r){
    return (((fact[n] * rfact[r]) % mod) * rfact[n-r]) % mod;}
*/
 
ll n,m,num,sum,ans,a,b,c,e,g,h,w,i,j,k,q;
ll t,d;
ll x[500005],y[500005],z[500005];
P table[500005];
string s;
ll in,out;

bool solve(ll a,ll b){
	//pe(a);p(b);
	bool ok = true;
	if(a > out || b > in){
		ok = false;
	}
	for(int i=0;i<n-1;i++){
		ll otherin,otherout;
		otherin = in + a - x[i];
		otherout = out + b - y[i];
		if(otherin < y[i] || otherout < x[i])ok = false;
	}
	return ok;
}
int main(){
    cin >> n;
    if(n == 2){
    	p(1);
    	return 0;
    }
    for(int i=0;i<n-1;i++){
    	cin >> x[i] >> y[i];
    	in += x[i];
    	out += y[i];
    }
    if(in > out){
    	a = 0;
    	b = in - out;
    }else{
    	a = out - in;
    	b = 0;
    }
    while(1){
    	bool isok = solve(a, b);
    	if(isok){
    		ans++;
    	}
    	a++;
    	b++;
    	if(a > out || b > in){
    		break;
    	}
    }
    p(ans);
    return 0;
}