#include <stdio.h>
#include <stdlib.h>

int main(void){
             int input = 0,
                 a = 1,
                 b = 1,
                 c = 3,
                 fino = 0,
                 fib = 0;
                 scanf("%d", &input);
                 while (c != input) {
                       fib = a + b;
                       a = b; b = fib;
                       c++;
                       if((fib % 2) == 0){
                               fino += fib;
                       }
                 }
                 printf("%d", fino);
                 system("PAUSE");	
                 return 0;
}