# include <string.h>
# include <stdio.h>
# define MAXN 80
/** metatropi dyadikon bits se arithmo **/

int bin2dec(char x[])
{
	int count=0;
	int i;
	for(i=0;i<strlen(x);i++)
	{
		if(x[i]=='1') count=2*count+1;
		else count = 2 * count;
	}
	return count;
}

/** elegxei an to x exei mono bits **/
int isBinary(char x[])
{
	int i;
	if(strlen(x)==0) return 0;
	for(i=0;i<strlen(x);i++)
	{
		/** an opoiodipote den einai 0,1 tote epistrefei 0**/
		if(!(x[i]=='0' || x[i]=='1')) return 0;
	}
	return 1;
}

int main()
{
	char bits[MAXN];
	int dec;
	do
	{
		printf("Doste enan dyadiko arithmo ?\n");
		gets(bits);
	}while(!isBinary(bits));
	dec=bin2dec(bits);
	printf("O dekadikos einai %d \n",dec);
	return 0;
}