#include <iostream>
#include <bits/stdc++.h>
#define t_states 3
#define f_states 1
#define alphabets 2
#define unknown_symbol 0
#define accepted 1
#define not_accepted 2

enum states {q0, q1, q2};
enum inputs {a, b};

int a_states[f_states] = {q2};
char characters[alphabets] = {'a', 'b'};
int transition_table[t_states][alphabets];
int current_state = q0;

void Transition()
{
   /* transition_table[q0][a] = q1;
    transition_table[q0][b] = q1;
    transition_table[q1][a] = q1;
    transition_table[q1][b] = q2;
    transition_table[q2][a] = q2;
    transition_table[q2][b] = q2;
    */
    transition_table[q0][a] = q1;
    transition_table[q0][b] = q1;
    transition_table[q1][a] = q1;
    transition_table[q1][b] = q2;
    transition_table[q2][a] = q2;
    transition_table[q2][b] = q0;
}

int DFA(char current_symbol)
{
    int i, j;
    for(i=0; i<alphabets; i++)
    {
        if(current_symbol == characters[i])
        {
            break;
        }
    }

    if(i == alphabets)
    {
        return unknown_symbol;
    }

    for(j=0; j<f_states; j++)
    {
        if((current_state = transition_table[current_state][i]) == a_states[j])
        {
            return accepted;
        }
    }

    return not_accepted;
}

int main()
{
    char user_input;
    int result;
    Transition();

    printf("Enter a string: ");

    while((user_input = getchar()) != '\n')
    {
        result = DFA(user_input);
        if(result == unknown_symbol)
        {
            break;
        }
    }
    switch(result)
    {
    case unknown_symbol:
        printf("Unknown Symbol\n");
        break;
    case accepted:
        printf("Accepted\n");
        break;
    case not_accepted:
        printf("Not Accepted\n");
        break;
    }

    return 0;
}