function gemstones(arr) {
    // Write your code here
    let count=0;
    let minerals=""
    let str=arr.join("");
    
    for(let i of str){
        if(!minerals.includes(i)){
             minerals+=i
        }
    }
    
    for (let i of minerals){
        let skip=false
        for(let j of arr){
            if(!j.includes(i)){
                skip=true
                break;
            }  
        }
        if(skip==false){
            count++  
        }
    }
    return count
}