My code adds all but the last number in a sequence of decimal numbers in a string,with each number separated by a comma why is this so ?
if s=1.2,3.3,4.5 only first two numbers are added

```
s=input("Please enter a sequence of comma seperated decimal numbers: ")
a=""
ans=0
i=0
for c in s:
    if c!="," :
        a+=s[i]
    else:
        ans+=float(a)
        a=""
    i+=1    
    if i==len(s):
        break
print("The sum of numbers is =",ans)

```