Problem:
Score : 100 points

Problem Statement

You are given a 4-character string S consisting of uppercase English letters.
Determine if S consists of exactly two kinds of characters which both appear twice in S.

Constraints

The length of S is 4.

S consists of uppercase English letters.

Input

Input is given from Standard Input in the following format:

S

Output

If S consists of exactly two kinds of characters which both appear twice in S, print Yes; otherwise, print No.

Sample Input 1

ASSA

Sample Output 1

Yes

S consists of A and S which both appear twice in S.

Sample Input 2

STOP

Sample Output 2

No

Sample Input 3

FFEE

Sample Output 3

Yes

Sample Input 4

FREE

Sample Output 4

No

Solution in C (Clang 3.8.0) (judge verdict: Wrong Answer)

#include<stdio.h>
int main(void){
int n,i,cnt=0;
scanf("%d",&n);
int A[n];
for(i=0;i<n;i++)
{
scanf("%d",&A[i]);
}

for(i=1;i<n-1;i++)
{
if((A[i-1]<A[i]&&A[i]<A[i+1])||(A[i]<A[i-1]&&A[i+1]<A[i]))
cnt++;
}
printf("%d",cnt);

return 0;
}