View Compilation Error

0_0_30308042_11716.cpp:4:1: error: expected ',' or ';' before 'const'
 const int maxn=500005;
 ^
0_0_30308042_11716.cpp: In function 'int main()':
0_0_30308042_11716.cpp:20:46: error: 'getInv2' was not declared in this scope
    dp[i+1]=(dp[i+1]+(r-s)%modd*getInv2(s,modd)%modd*dp[x]%modd+modd)%modd;
                                              ^