function main(input){
    inputNA = input.split('\n');
    inputN = parseInt(inputNA[0]);
    inputA = inputNA[1].split(' ');
    out='Yes';

    for(i=0;i<inputN;i++){
        for(j=i+1;j<inputN;j++){
            if(inputA[i]==inputA[j]){
                out='NO';
            }
            if(out=='NO'){
                break;
            }
        }
        if(out=='NO'){
            break;
        }
    }

    console.log(out);

}

main(require("fs").readFileSync("/dev/stdin", "utf8"));