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# Nearest prime less than given number n C++

We are given a number n, we need to find the nearest prime number that is less than n. We can find the number easily if we start checking from the n - 1. Let's see some examples.

**Input**

10

**Output**

7

## Algorithm

- Initialise the number n.
- Write a loop that iterates from n - 1 to 1
- Return the first prime number that you found

- Return -1 if you didn't find any prime that's less than given n

## Implementation

Following is the implementation of the above algorithm in C++

#include <bits/stdc++.h> using namespace std; bool isPrime(int n) { if (n == 2) { return true; } for (int i = 2; i <= ceil(sqrt(n)); i++) { if (n % i == 0) { return false; } } return true; } int getNearestPrimeNumber(int n) { for (int i = n - 1; i > 1; i--) { if (isPrime(i)) { return i; } } return -1; } int main() { int n = 20; cout << getNearestPrimeNumber(n) << endl; return 0; }

## Output

If you run the above code, then you will get the following result.

19

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