Substring error: System.Argued tofrangeexception

Question

I couldn’t understand how the calculation of substring in c#;

The variable below contains 150 characters, I use the substring to receive a part of it, but an exception occurs even being within reach. How the parameters of substring?

string conteudo = "Morbi laoreet congue eros, eu elementum lacus dapibus sit amet. Praesent scelerisque, sapien ut efficitur dapibus, ante ligula aliquam lorem, in faucibus ante tortor ac turpis. Fusce lobortis enim ac dui sodales, suscipit ultricies odio dapibus. Sed semper sapien eu tortor imperdiet dapibus. Nunc dictum pellentesque nisi, ac posuere felis luctus in. Sed eu est quis massa pretium condimentum vel sed justo. Aliquam pellentesque in tellus at tristique.";

conteudo.Substring(70,100); //erro