#include <stdio.h>
 
int main() {
    int arr[] = {1, 2, 4, 5, 6}; // Example array with one number missing
    int n = 6;  // The array should contain numbers from 1 to n → here n = 6
    int size = sizeof(arr) / sizeof(arr[0]);
 
    printf("%d", size);
 
    int total = n * (n + 1) / 2;  // Sum of numbers from 1 to n
    int sum = 0;
 
    for (int i = 0; i < size; i++) {
        sum += arr[i];
    }
 
    int missingNumber = total - sum;
 
    printf("The missing number is: %d\n", missingNumber);
 
    return 0;
}
 

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