UVA 575 Skew Binary

#include<iostream>
#include<cstring>
#include<string>
#include<cmath>

using namespace std;

int main()
{
string num;
long long len,i;
long long sum=0;
long long j;
j=1;

while(cin>>num)
{
if(num=="0") break;
len=num.length();

for(i=len-1; i>=0; i--)
{
if(num[i]=='1') sum=sum + (pow(2,j)-1);
else if(num[i]=='2') sum= sum+  (2 * (pow(2,j)-1));
j++;
}
cout<<sum<<endl;
sum=0;
j=1;


}
}