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: Accepted)

#include<stdio.h>

void main(){
	char string[5];
	scanf("%s",&string);
	int judge=0;
	if(string[0] == string[1]){
		if(string[2] == string[3]){
			if(string[0] != string[2]){
				judge = 1;
			}
		}
	}
	else if(string[0] == string[2]){
		if(string[1] == string[3]){
			if(string[0] != string[1]){
				judge = 1;
			}
		}
	}
	else if(string[0] == string[3]){
		if(string[1] == string[2]){
			if(string[0] != string[1]){
				judge = 1;
			}
		}
	}
	
	if(judge == 1) printf("Yes");
	else printf("No");
}