Thanks for trying

int main(){

int t;
cin >> t;
for(int a0 = 0; a0 < t; a0++){
    int n, y, z, flag = -1;
    cin >> n;
    z = n;
    if(z <= 0)
        cout<<"-1\n";
    else
 {
    if(z%3 == 0)
        {
        cout<< string(z,'5')<<"\n";
    }
    while(z%3 != 0)
        {
        z -= 5;
     if(z<0)
            {
            cout<<"-1\n";
            break;
        }
    else
        {
        cout<<string(z,'5')<<string((n-z),'3')<<"\n";;
    }
    }
 }
}
return 0;

}

This is what i ment exactly, but still not working for large inputs :(