## COCI '10 Contest 4 #5 Dugovi

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Points: 12 (partial)
Time limit: 1.0s
Memory limit: 32M

Problem types

In a little town called Križ live people. Each of them has borrowed some money from exactly one other inhabitant. Now the time has come to pay back all the debts, but the problem is that everybody has spent all of their money!

The major of Križ has decided to solve this problem. The town will give money to a few people so that they can pay back their debts. When some people get their money back, a chain reaction is started - for example: person gets money from the city. Person uses that money to pay the debt toward person . Person then uses that money to pay the debt towards person etc. If person didn't have enough money to pay back the debt, they wait until they get enough. If they have more than enough money, person will keep what is left after payback.

Another example: if two people live in Križ, and they owe to each other, the town will give to one of them so they can pay back the debt to the other one.

Your task is to calculate the minimum total amount of money the town has to give to some subset of the inhabitants so that after the payback protocol described above all debts are paid.

#### Input Specification

First line of input contains one integer , number of inhabitants of Križ. They are numbered from to .

The following lines contain two integers, separated by space. In of those lines, first number - represents the id of the person person owes money to , and second represents the amount of the debt in .

#### Output Specification

First and only line of output should contain one integer - the minimum total amount of money the town has to give to its inhabitants so all debts are paid.

#### Sample Input 1

4
2 100
1 100
4 70
3 70

#### Sample Output 1

170

#### Sample Input 2

3
2 120
3 50
2 80

#### Sample Output 2

150

#### Sample Input 3

5
3 30
3 20
4 100
5 40
3 60

#### Sample Output 3

110