is-prime-day.cpp

#include <iostream>
#include <cmath>
using namespace std;

bool isPrime(int num){
    if (num <= 1) return false;
    
    for(int i = 2; i <= sqrt(num); i++){
        if (num % i == 0) {
            return false;
        }
    }
    return true;
}

void isPrimeDay(string date){
    int dateLength = date.length();
    
    for (int i = 0; i < dateLength; i++){
        if (!isPrime(stoi(date.substr(i, dateLength)))) {
            cout << "This date is not prime day.";
            return 0;
        }
    }

    cout << "It's a prime day!";
    return 0;
}

int main(){
    string num;
    cin >> num;

    isPrimeDay(num);
}