View Compilation Error

0_0_21856004_25410.cpp: In function 'int main()':
0_0_21856004_25410.cpp:81:13: error: 'res' was not declared in this scope
             res = (res + len*(len+1)/2) % M;
             ^
0_0_21856004_25410.cpp:83:17: error: 'res' was not declared in this scope
         cout << res << endl;
                 ^