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 (GCC 5.4.1) (judge verdict: Runtime Error)

#include<stdio.h>
int main()
{
	int p[100],n,num=0;
	scanf("%d",&n);
	for(int i=1;i<=n;i++){
		scanf("%d",&p);
		if(p[i-1]<p[i] && p[i]<p[i+1] || p[i-1]>p[i] && p[i]>p[i+1]){	
			num++;
		}
	}
	printf("%d\n",num);	
	return 0;
}