I am trying to get the count of elements in a nested list after iterating over it. However, when the element i'm looking for is not in the list, I want the code to return me `0`. But it gives me a blank output instead of `0`.How can I solve it?

```
s=[['F1','S1'],['F2','S2'],['F3','S3'],['F1','S2'],['F2','S3'],['F3','S2'],['F2','S1'],['F4','S1'],['F4','S3'],['F5','S1']]
F=[]
S=[]
for a,b in s:
    F.append(a)
    S.append(b)
for i in s:
    if i[0]=='F1' and i[1]=='S1':
        print('P(F=F1|S==S1):',s.count(i),'/',S.count('S1'))
    if i[0]=='F1' and i[1]=='S2':
        print('P(F=F1|S==S2):',s.count(i),'/',S.count('S2'))
    if i[0]=='F1' and i[1]=='S3':
        print('P(F=F1|S==S3):',s.count(i),'/',S.count('S3'))

```

the output I get is :  

```
P(F=F1|S==S1): 1 / 4
P(F=F1|S==S2): 1 / 3

```

I don't getout put when `i[0]=='F1'` and `i[1]=='S3'` .