import java.util.*;
public class euler {
    
    public static void main(String[] args) {
    	System.out.println("Euler question 1: " + question1());
    	System.out.println("Euler question 2: " + question2());
    	System.out.println("Euler question 4: " + question4());
    	System.out.println("Euler question 5: " + question5());
    	System.out.println("Euler question 6: " + question6());
    	System.out.println("Euler question 7: " + question7()); 
    	System.out.println("Euler question 9: " + question9());
    	System.out.println("Euler question 10: " + question10());
    }
    
    public static int question1() {
    	int a = 0;
        for(int i = 0; i < 1000; i++){
            if ((i % 3 == 0) || (i % 5 == 0 ))
                a += i;
        }
        return a;
    }
    public static int question2() {
    	int a = 0;
    	for (int i = 0; fib(i) < 4000000; i++) {
    		if (fib(i) % 2 == 0)
    			a += fib(i);
    	}
    	return a;
    }
    public static long fib(long i){
        if (i > 1)
            return fib(i - 1) + fib(i - 2);
        return i;
	}
	
	public static int question4() {
		int answer = 0;
		for(int i = 100; i < 1000; i++) {
			for(int j = 100; j < 1000; j++) {
				if (isPalindrome(i*j)) {
					if (i*j > answer)
					answer = i*j;
				}
			}
		}
		return answer;
	}
	
	public static boolean isPalindrome(int l) {
		if(l == Integer.parseInt(getReverse(Integer.toString(l))))
			return true;
		return false;
	}
	
	public static String getReverse(String arg) {
		String tmp = null;
		if (arg.length() == 1) {
			return arg;
		} else {
			String lastChar = arg.substring(arg.length()-1,arg.length());
			String remainingString = arg.substring(0, arg.length() -1);
			tmp = lastChar + getReverse(remainingString);
			return tmp;
		}
	}
	
	public static long question5() {
		int count = 0, i = 1;
		for (i = 1; count != 20; i++) {
			for (int factor = 1; factor < 21; factor++) {
				if (i % factor == 0)
					count++;
			}
			if (count != 20)
				count = 0;
		}
		return i - 1;
	}
	public static long question6() {
		int a = 0, b = 0;
		for (int i = 0; i <= 100; i++) {
			a += (i * i);
		}
		for (int i = 0; i <= 100; i++) {
			b += i;
		}
		return (b * b) - a;
	}
	public static long question7() {
		int k = 0, i = 2;
		for (i = 2; k < 10001; i++) {
			if (isPrime(i))
				k++;
		}
		return i - 1;
	}
	
	public static boolean isPrime(long n) {
    	for (long i = 2; i < n; i++) {
    		if(n % i == 0)
    			return false;
    	}
    	return true;
    }
    public static long question9() {
    	for (int a = 1; a < 1000; a++) { //a < 1000 is just ... good enough.
    		for (int b = 1; b < 1000; b++) { //same here.
    			if (isTriple(a, b)) {
    				int c = (int)Math.sqrt((a * a) + (b * b));
    				if (a + b + c == 1000)
    					return a * b * c;
    			}
    		}
    	}
    	return 0;
    }
    
    public static boolean isTriple(int c, int d) {
    	if (Math.sqrt((c * c) + (d * d)) == (int)Math.sqrt((c * c) + (d * d)))
    		return true;
    	return false;
    }
    public static long question10() {
    	int answer = 0;
    	for (int i = 0; i < 2000000; i++) {
    		if (isPrime(i))
    			answer += i;
    	}
    	return answer;
    }
}