#include?
#include?
#include?
#include?

#define?nbuf?65536

static?inline?double?sq（double?x）?{return?x*x;}

void?fileerror（const?char?*filename?FILE?*file）
{
????fclose（file）;
????fprintf（stderr?“error?reading?file?%s\n“?filename）;
????exit（4）;
}

void?openerror（const?char?*filename）
{
????fprintf（stderr?“error?opening?file?%s\n“?filename）;
????exit（3）;
}

FILE?*openandfindlastbeefens（const?char?*filename?char?*buf）
{
????FILE?*f;
????unsigned?long?int?ulastu;
????
????f?=?fopen（filename?“r“）;
????if（!f）?openerror（filename）;
????
????u?=?1;
????while（fgets（bufnbuff）?&&?!strstr（buf“BEEFens“））?u++;
????if（!strstr（buf“ensemble?energies“））?fileerror（filename?f）;

????do?{
	lastu?=?u;
	u++;
	while（fgets（bufnbuff）?&&?!strstr（buf“BEEFens“））?u++;
????}?while（strstr（buf“ensemble?energies“））;
????
????if（fseek（f0SEEK_SET））?fileerror（filename?f）;
????
????for（u=0;u????
????return?f;
}


int?main（int?argc?char?**argv）
{
????char?buf[nbuf];
????double?*samples;
????FILE?*dftout;
????double?de;
????int?nsamples;

????if（argc?????{
	fprintf（stderr?“usage:?%s?factor1?outputfile1?...?factorN?outputfileN\n“?argv[0]）;
	return?1;
????}

????dftout?=?openandfindlastbeefens（argv[2]?buf）;
????nsamples?=?strtol（strstr（buf“BEEFens“）+7?NULL?10）;

????samples?=?（double?*）?malloc（nsamples*sizeof（double））;
????if（!samples）
????{
	fclose（dftout）;
	fputs（“not?enough?memory?for?ensemble?energies\n“?stderr）;
	return?2;
????}

????d?=?strtod（argv[1]?NULL）;
????for（int?j=0;j????{
	if（!fgets（bufnbufdftout））?fileerror（argv[2]?dftout）;
	samples[j]?=?d*strtod（buf?NULL）;
????}
????fclose（dftout）;
????for（int?i=3;i????{
	d?=?strtod（argv[i]?NULL）;
	dftout?=?openandfindlastbeefens（argv[i+1]?buf）;
	for（int?j=0;j	{
	????if（!fgets（bufnbufdftout））?fileerror（argv[i+1]?dftout）;
	????samples[j]?+=?d*strtod（buf?NULL）;
	}
	fclose（dftout）;
????}

????d?=?samples[0];
????for（int?i=1;i????d?/=?（double）?nsamples;
????e?=?sq（samples[0]-d）;
????for（int?i=1;i????free（samples）;

????printf（“%.5g?standard?deviation\n“?sqrt（e/nsamples））;

????return?0;
}