### PROBLEM LINK:

**Author:** Kamil Debowski

**Tester:** Niyaz Nigmatullin

**Editorialist:** Kamil Debowski

### DIFFICULTY:

CAKEWALK

### PREREQUISITES:

none

### PROBLEM

Given a sequence of strings “cookie” and “milk”, you should check whether after each “cookie” the next string is “milk”.

### EXPLANATION

We should implement exactly what is written in the statement.

For each string s[i] if it is “cookie” then we must check if s[i+1] is “milk”.

So the answer will be “NO” in two cases (assuming that s[i] == “cookie”):

- i = N, what means that s[i] is the last string
- s[i+1] == "cookie"

Let’s see the pseudocode of this intended solution:

```
bool answer = true
for i = 1 to N do
if (s[i] == "cookie") then
if (i == N or s[i+1] != "milk") then
answer = false
if (answer) then
print("YES")
else
print("NO")
```

### POSSIBLE MISTAKES

One wrong approach is to think that the answer is “NO” if and only if some two consecutive strings are both equal to “cookie”.

For example, (“milk”, “cookie”, “cookie”, “milk”) indeed gives answer “NO”.

The last of given in the statement example test cases shows that this claim isn’t correct.

The answer is “NO” also if the last string is “cookie”.

In such a situation Limak indeed eats a cookie and doesn’t drink milk in the next minute.

### ALTERNATIVE APPROACH

A mistake described in the previous paragraph can be fixed by additionally checking the last string of the given sequence.

So we can get a slightly different implementation:

```
bool answer = true
for i = 1 to N-1 do #we iterate to N-1 only!
if (s[i] == "cookie" and s[i+1] == "cookie") then
answer = false
if (s[N] == "cookie") then
answer = false
```

### AUTHOR’S AND TESTER’S SOLUTIONS:

Setter’s solution can be found here.

Tester’s solution can be found here.