foo.cc: In function 'int main()':
foo.cc:29:50: warning: format '%d' expects argument of type 'int', but argument 2 has type 'std::__cxx11::basic_string<char>::size_type {aka long unsigned int}' [-Wformat=]
  printf("%d",len + 1 - str.rfind(str.substr(1,j)));
              ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^

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