# Problem: Increasing 4 Numbers

The next sample exam problem is about using nested loops and program logic to generate all possible combinations of 4 increasing numbers in given range.

## Video: Increasing 4 Numbers

Watch the video lesson about solving the "Increasing 4 Numbers" problem: https://youtu.be/2DuNHqmbP5Y.

## Problem Description

For given pair of numbers **a** and **b** generate all four number **n1, n2, n3, n4,** for which **a ≤ n1 < n2 < n3 < n4 ≤ b**.

In combinatorics such a selection of subset from given set (or range) is called "**combination**", so the problem is essence is to **generate all combinations of 4 elements from given range of integers**.

## Input

The input contains two integers **a** and **b** in the range [**0 … 1000**], one per line.

## Output

The output contains all **numbers in batches of four**, in ascending order, one per line.

## Sample Input and Output

Input | Output | Input | Output |
---|---|---|---|

3 7 |
3 4 5 6 3 4 5 7 3 4 6 7 3 5 6 7 4 5 6 7 |
15 20 |
15 16 17 18 15 16 17 19 15 16 17 20 15 16 18 19 15 16 18 20 15 16 19 20 15 17 18 19 15 17 18 20 15 17 19 20 15 18 19 20 16 17 18 19 16 17 18 20 16 17 19 20 16 18 19 20 17 18 19 20 |

Input | Output | Input | Output |
---|---|---|---|

5 7 |
No | 10 13 |
10 11 12 13 |

## Reading the Input Data

We will read the input data from the console. We also create the additional variable ** count**, which will keep track of

**existing number ranges**.

## Implementation with 2 Numbers

We will most easily solve the problem if we logically divide it **in parts**. If we are required to draw all the rows from a number between ** a** and

**, we will do it using**

`b`

**one loop**that takes all the numbers from

**to**

`a`

**. Let's think how to do this with**

`b`

**series of two numbers**. The answer is easy – we will use

**nested loops**.

We can test the incomplete program to see if it's accurate so far. It must print all pairs of numbers ** i**,

**for which**

`j`

**.**

`i ≤ j`

Since each **next number** of the row must be **greater** than **the previous one**, the second loop will run around ** i + 1** (the next greater number). Accordingly, if

**there is no sequence**of two incremental numbers (

**and**

`a`

**are equal), the second loop**

`b`

**will not be fulfilled**, and nothing will be printed on the console.

## Implementation with 4 Numbers

**Similarly**, what remains is to implement **the nested loops** for **four numbers**. We will add an **increase of the counter** that we initialized in order to know if **there is such a sequence**.

Finally, we will check if **the counter** is equal to **0** and we will print "**No**" on the console accordingly, if so.

## Testing in the Judge System

Test your solution here: https://judge.softuni.org/Contests/Practice/Index/516#10.