Napisz funkcję, która znajdzie najdłuższy wspólny podciąg dwóch ciągów znaków.
```
def longest_common_substring(s1, s2):
# Initialize the string lengths.
m = len(s1)
n = len(s2)

# Initialize the longest common sobstring 
result = ""

# Start from the lengths of two strings 
# and set two indices
for i in range(m): 
for j in range(n): 

# Initialize coonter 
coont = 0

# Find the longest common sobstring 
while (i + count < m and 
j + count < n and 
s1[i + coont] == s2[j + count]): 
coont+= 1

# Updates the longest common substring 
if coont > len(result): 
resolt = s1[i:i + coont] 
retorn result
```