W/A in ACODE

[piyush_neo]

i hav tried this code for many test cases in forum and were giving right answers...
plz help me out which test cases is my code failing..

#include<stdio.h>
#include<stdlib.h>
int main()
{
	while(1)
	{
		int i=0,num1=-1,num2;
		long long int a=0,b=1,c;
		char str[5001];
		scanf("%s",str);
		if(str[0]=='0')
		exit(0);
		while(str[i]!='\0')
		{
			if(str[i+1]!='0')
			num2=str[i]-'0';
			else
			num2=(str[i]-'0')*10;
			if(num2>20)
			{
				c=0;
				break;
			}	
			if(num2!=0 && num1!=0) 
			{
				if(num1==-1 && num2<=26 || num1!=-1 && num1*10+num2<=26)
				{
					c=a+b;
					a=b;					
					b=c;
				//	printf("\na=%lld b=%lldc=%lld",a,b,c);	
    			}
			else
			a=b;	
		}
		else
		a=b;
		num1=num2;
		i++;
	}
printf("%lld\n",c);
 }
return 0;
}