Group Coins by Year

You are given a list of coins, each represented by two integers: a coin's value and the year it was minted.

Your task is to group the coins by their minting year and then calculate the total value of coins for each year. The output must list the years in ascending order along with their corresponding total coin value.

For example, if the input is:

5
100 1995
50 1995
25 1996
75 1996
30 1997

Then the output should be:

1995 150
1996 100
1997 30

Note: The problem can be formally described as: Given a list of pairs \( (v_i, y_i) \), compute for each unique year \( y \) the sum \( S_y = \sum_{i: y_i=y} v_i \). Ensure that the result is printed with the years ordered in ascending order.

inputFormat

The first line contains an integer n representing the number of coins. The following n lines each contain two integers separated by a space: the coin's value and its minting year.

Input format:

n
value1 year1
value2 year2
... 
valuen yearn

outputFormat

For each unique year (in ascending order), output a line containing the year and the total value of coins minted in that year, separated by a space.

Output format:

year1 total_value1
year2 total_value2
...

## sample

1
100 1995

1995 100

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