changes to your code and its working for all test cases

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
        {
        if(z%3==0)
             cout<<string(z,'5')<<string((n-z),'3')<<"\n";
    }
}


}
}
return 0;

}