#include <iostream>
using namespace std;

int gcd(int x,int y){
   if((x == 0) || (y == 0)) return 0;
   while(x != y){
      if(x > y) x -= y;
      else y -= x;
   }
   return x;
}

int lcm(int x,int y){
   if((x == 0) || (y == 0)) return 0;
   return (x * y / gcd(x,y));
}

int main(){
   int ans = 0,n,lcmkeep;
   cin >> n;
   int a[n],b[n],space[n];
   for(int i = 0;i < n;i++) cin >> a[i] >> b[i];
   for(int i = 0;i < n;i++) space[i] = a[i] + 4 * b[i];
   for(int i = 0;i < n;i++){
      if(i == 0){
         lcmkeep = lcm(space[i],space[i + 1]);
         i += 2;
      }else lcmkeep = lcm(lcmkeep,space[i]);
   }
   for(int i = 0;i < n;i++) ans += lcmkeep - space[i];
   cout << ans << endl;
}