import java.util.*;
import java.lang.*;
import java.math.*;

class Main
{
	public static void main (String[] args) throws java.lang.Exception
	{
		long sum = 0;
		for(long i = 0; ; i++) {
			long n = fib(i);
			if(n >= 4000000) {
				break;
			}
			sum += n;
		}
		System.out.println("sum : " + sum );
	}
	
	private static long fib(long n) {
		if(n == 0 || n == 1) {
			return 1;
		}
		
		long n0 = 1;
		long n1 = 1;
		long curr = n0 + n1;
		for(long i = 1; i < n; i++) {
			curr = n0 + n1;
			n0 = n1;
			n1 = curr;
		}
		
		return curr;
	}
}