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

//template
#define rep(i,a,b) for(int i=(a);i<(b);i++)
#define rrep(i,a,b) for(int i=(a);i>(b);i--)
#define ALL(v) (v).begin(),(v).end()
typedef long long int ll; typedef pair<ll, ll> P;
template<class T> inline bool chmax(T& a, T b) { if (a < b) { a = b; return 1; } return 0; }
template<class T> inline bool chmin(T& a, T b) { if (a > b) { a = b; return 1; } return 0; }
template<typename A,size_t N,typename T>void Fill(A(&array)[N],const T &val){fill((T*)array, (T*)(array+N), val);}
const int inf = 0x3fffffff; const ll INF = 0x3fffffffffffffff;
//template end



int main(){
    int n; scanf("%d",&n);
    vector<P> a(n-1); int sum[2]={};
    rep(i,0,n-1){
        scanf("%d%d",&a[i].first,&a[i].second);
        sum[0]+=a[i].first; sum[1]+=a[i].second;
    }
    int ans=0;
    rep(i,0,sum[0]+1){
        int rem=sum[1]+i-sum[0]; if(rem<0)continue;
        bool f=1;
        rep(i,0,n-1)if(a[i].second>sum[0]+rem-a[i].first)f=0;
        if(f)ans++;
    }
    printf("%d\n",ans);
    return 0;
}