#include<bits/stdc++.h>
//ios::sync_with_stdio(false);cin.tie(0);
using namespace std;
typedef long long ll;
typedef unsigned long long ull;
typedef pair<int,int> pii;
typedef pair<pii,int> ppii;
typedef pair<int,pii> pipi;
typedef pair<ll,ll> pll;
typedef pair<pll,ll> ppll;
typedef pair<ll,pll> plpl;
typedef tuple<ll,ll,ll> tl;
ll mod=1000000007;
ll mod2=998244353;
ll mod3=1000003;
ll mod4=998244853;
ll inf=1000000000000000000;
double pi=2*acos(0);
#define rep(i,m,n) for(ll i=m;i<n;i++)
#define rrep(i,n,m) for(ll i=n;i>=m;i--)
int dh[4]={1,-1,0,0};
int dw[4]={0,0,1,-1};
int ddh[8]={-1,-1,-1,0,0,1,1,1};
int ddw[8]={-1,0,1,-1,1,-1,0,1};
ll lmax(ll a,ll b){
    if(a<b)return b;
    else return a;
}
ll lmin(ll a,ll b){
    if(a<b)return a;
    else return b;
}
ll gcd(ll a,ll b){
    if(a<b)swap(a,b);
    if(b==0)return a;
    if(a%b==0)return b;
    return gcd(b,a%b);
}
ll Pow(ll n,ll k){
    ll ret=1;
    ll now=n;
    while(k>0){
        if(k&1)ret*=now;
        now*=now;
        k/=2;
    }
    return ret;
}

int main(){
    ios::sync_with_stdio(false);cin.tie(0);
    ll n;cin>>n;
    ll a[n],b[n];
    ll sa=0,sb=0;
    rep(i,1,n){
        cin>>a[i]>>b[i];
        sa+=a[i];
        sb+=b[i];
    }
    ll ans=0;
    rep(i,0,sb+1){
        ll jj=i+sa-sb;
        if(jj<0||jj>sa)continue;
        ll r=0;
        rep(j,1,n){
            ll ta=sa+i;
            ll tb=sb+jj;
            ta-=a[j];
            tb-=b[j];
            if(ta<b[j]||tb<a[j]){
                r=1;
                break;
            }
        }
        if(r==0)ans++;
        //cout<<ans<<endl;
    }
    cout<<ans<<endl;
}