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#include <stdio.h>

// Define the states of the FSM
typedef enum { Q0, Q1, REJECT } State;

// Transition function for the FSM
State transition(State currentState, char input) {
    switch (currentState) {
        case Q0:
            if (input == 'a') {
                return Q1;  // Transition from Q0 to Q1 on 'a'
            } else {
                return REJECT;  // Transition to REJECT on any other input
            }
        case Q1:
            return Q1;  // Stay in Q1 for any input after 'a'
        default:
            return REJECT;  // Stay in REJECT state for any input
    }
}

// Function to check if the string starts with 'a'
int startsWithA(const char *str) {
    State currentState = Q0;  // Start at the initial state (Q0)
    int i = 0;

    // Process each character in the input string
    while (str[i] != '\0') {
        currentState = transition(currentState, str[i]);  // Get the next state
        if (currentState == REJECT) {
            return 0;  // If in REJECT state, return false (0)
        }
        i++;
    }

    // Return 1 (true) if the final state is Q1, otherwise return 0 (false)
    return (currentState == Q1);
}

int main() {
    char input[100];

    // Prompt the user to enter a string
    printf("Enter a string: ");
    scanf("%s", input);

    // Check if the string starts with 'a'
    if (startsWithA(input)) {
        printf("The string starts with 'a'.\n");
    } else {
        printf("The string does not start with 'a'.\n");
    }

    return 0;
}