Language: Java

import java.io.InputStream;
import java.io.IOException;
import java.io.PrintWriter;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Comparator;
import java.util.InputMismatchException;
import java.util.NoSuchElementException;
import java.math.BigInteger;

public class Main{

static PrintWriter out;
static InputReader ir;
static int[] p=new int[101],q=new int[101],r=new int[101],b=new int[101],par=new int[101];

static void solve(){
 int n;
 while((n=ir.nextInt())!=0){
  for(int i=0;i<n;i++){
   p[i]=ir.nextInt();
   q[i]=ir.nextInt();
   r[i]=ir.nextInt();
   b[i]=ir.nextInt();
   par[r[i]]=par[b[i]]=i+1;
   long g=gcd(p[i],q[i]);
   p[i]/=(int)g;
   q[i]/=(int)g;
  }
  int now=1;
  while(par[now]!=0) now=par[now];
  out.println(dfs(now));
  Arrays.fill(par,0);
 }
}

public static int dfs(int m){
 int now=m-1;
 if(r[now]==0&&b[now]==0) return (long)p[now]+(long)q[now];
 if(r[now]==0){
  long bb=dfs(b[now]);
  return bb/gcd(q[now],bb)*(p[now]+q[now]);
 }
 if(b[now]==0){
  long rr=dfs(r[now]);
  return rr/gcd(p[now],rr)*(p[now]+q[now]);
 }
 long bb=dfs(b[now]),rr=dfs(r[now]);
 int g=gcd(bb*p[now],rr*q[now]);
 return rr*(long)q[now]/g*bb+bb*(long)p[now]/g*rr;
}

public static long gcd(long a,long b){
 if(b==0) return a;
 return gcd(b,a%b);
}

public static void main(String[] args) throws Exception{
 ir=new InputReader(System.in);
 out=new PrintWriter(System.out);
 solve();
 out.flush();
}

static class InputReader {
 private InputStream in;
 private byte[] buffer=new byte[1024];
 private int curbuf;
 private int lenbuf;

 public InputReader(InputStream in) {this.in=in; this.curbuf=this.lenbuf=0;}
 
 public boolean hasNextByte() {
  if(curbuf>=lenbuf){
   curbuf= 0;
   try{
    lenbuf=in.read(buffer);
   }catch(IOException e) {
    throw new InputMismatchException();
   }
   if(lenbuf<=0) return false;
  }
  return true;
 }

 private int readByte(){if(hasNextByte()) return buffer[curbuf++]; else return -1;}
 
 private boolean isSpaceChar(int c){return !(c>=33&&c<=126);}
 
 private void skip(){while(hasNextByte()&&isSpaceChar(buffer[curbuf])) curbuf++;}
 
 public boolean hasNext(){skip(); return hasNextByte();}
 
 public String next(){
  if(!hasNext()) throw new NoSuchElementException();
  StringBuilder sb=new StringBuilder();
  int b=readByte();
  while(!isSpaceChar(b)){
   sb.appendCodePoint(b);
   b=readByte();
  }
  return sb.toString();
 }
 
 public int nextInt() {
  if(!hasNext()) throw new NoSuchElementException();
  int c=readByte();
  while (isSpaceChar(c)) c=readByte();
  boolean minus=false;
  if (c=='-') {
   minus=true;
   c=readByte();
  }
  int res=0;
  do{
   if(c<'0'||c>'9') throw new InputMismatchException();
   res=res*10+c-'0';
   c=readByte();
  }while(!isSpaceChar(c));
  return (minus)?-res:res;
 }
 
 public long nextLong() {
  if(!hasNext()) throw new NoSuchElementException();
  int c=readByte();
  while (isSpaceChar(c)) c=readByte();
  boolean minus=false;
  if (c=='-') {
   minus=true;
   c=readByte();
  }
  long res = 0;
  do{
   if(c<'0'||c>'9') throw new InputMismatchException();
   res=res*10+c-'0';
   c=readByte();
  }while(!isSpaceChar(c));
  return (minus)?-res:res;
 }

 public double nextDouble(){return Double.parseDouble(next());}

 public int[] nextIntArray(int n){
  int[] a=new int[n];
  for(int i=0;i<n;i++) a[i]=nextInt();
  return a;
 }

 public long[] nextLongArray(int n){
  long[] a=new long[n];
  for(int i=0;i<n;i++) a[i]=nextLong();
  return a;
 }

 public char[][] nextCharMap(int n,int m){
  char[][] map=new char[n][m];
  for(int i=0;i<n;i++) map[i]=next().toCharArray();
  return map;
 }
}
}

Compiler output:
Main.java:39: error: incompatible types: possible lossy conversion from long to int
 if(r[now]==0&&b[now]==0) return (long)p[now]+(long)q[now];
                                             ^
Main.java:42: error: incompatible types: possible lossy conversion from long to int
  return bb/gcd(q[now],bb)*(p[now]+q[now]);
                          ^
Main.java:46: error: incompatible types: possible lossy conversion from long to int
  return rr/gcd(p[now],rr)*(p[now]+q[now]);
                          ^
Main.java:49: error: incompatible types: possible lossy conversion from long to int
 int g=gcd(bb*p[now],rr*q[now]);
          ^
Main.java:50: error: incompatible types: possible lossy conversion from long to int
 return rr*(long)q[now]/g*bb+bb*(long)p[now]/g*rr;
                            ^
5 errors