#include <stdio.h>
#include <inttypes.h>

uint64_t mid (uint64_t a, uint64_t b, uint64_t res)
{
  if (b == 0){ if (a > 2) return mid (a-2, b  , res+1); else return res;}
  if (a == 0){ if (b > 2) return mid (a  , b-2, res+1); else return res;}
  return mid (a-1, b-1, res+1);
}

int main(void) {
	printf("%"PRIu64, mid(20, 13, 0));
	return 0;
}