#include <assert.h>
 
int mod_256(int x)
{
	if(x >= 0) { return (int)(unsigned char)x; }
	else { return -(int)(unsigned char)-x; }
}
 
int main()
{
	assert(mod_256(257) == 257 % 256);
	assert(mod_256(-257) == -257 % 256);
	return 0;
}