function marsExploration(s: string): number {
    const length = s.length;
    let changedChars = 0;
    
    for (let i = 0; i < length; i++) {
        const originalChar = (
            i % 3 === 0 ||
            (i + 1) % 3 === 0
        )  ? "S" : "O";
        if (s[i] !== originalChar) changedChars ++;
        
    }
    
    return changedChars;
}