void FSM_ba(int in,     // FSM input: 0 - a, 1 - b
            int out) {  // FSM output: 0 - not found, 1 - found

int state = 0;          // FSM state: 0 - S0, 1 - Sa, 2 - Sb, 3 - SA

while(1) {
    switch(state) {
        case 0:
            out = 0;
            break;

        case 1:
            out = 0;
            break;

        case 2:
            out = 0;
            break;

        case 3:
            out = 1;
            break:
    }
    
    read_inputs();

    switch(state) {
        case 0:
            if(in == 0)
                state = 1;
            else
                state = 2;
            break;

        case 1:
            if(in == 0)
                state = 1;
            else
                state = 2;
            break;

        case 2:
            if(in == 0)
                state = 3;
            else
                state = 2;
            break;

        case 3:
            if(in == 0)
                state = 1;
            else
                state = 2:
            break:
    }
}