#include <iostream>
int main(){
    int a,ans=0,x=0,y=0;
    scanf("%d",&a);
    int b[a-1],c[a-1];
    for(int i=0;i<a-1;i++){
        scanf("%d %d",&b[i],&c[i]);
        x+= *(b+i);
        y+= *(c+i);
    }
    for(int p = 0;p <= y;p++){
        int q = (x + p) - y;
        bool good = q >= 0;
        for(int i = 0;i< a-1;i++){
            if(b[i] > q + y -c[i]){
                good = false;
            }
        }
        ans += good;
    }
    std::cout << ans;
    return 0;
}