PROGRAMMING:1-9. Input 3 integers and output their sum

Write a program to display the sum of three integers read as follows.
```
Please enter three integers.
Integer 1:7 (enter)
Integer 2:15 (enter)
Integer 3:23 (enter)
The sum of them is 45.
```
###Input format:
Enter an integer at each prompt and press enter.
###Output format:
Please refer to the stem description.
###Input example:
```in
seven
fifteen
twenty-three
```
###Output example:
```out
Please enter three integers.
Integer 1: integer 2: integer 3: their sum is 45.
```







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