View Compilation Error

0_0_31553256_10986.cpp: In function 'int main()':
0_0_31553256_10986.cpp:13:15: error: too many arguments to function 'long long int f1(int)'
   sum=f1(n1,n2);
               ^
0_0_31553256_10986.cpp:8:6: note: declared here
  ll  f1(int x);
      ^
0_0_31553256_10986.cpp:15:3: error: expected ';' before 'if'
   if(z==1)sum=1;
   ^
0_0_31553256_10986.cpp: At global scope:
0_0_31553256_10986.cpp:23:14: error: 'x2' has not been declared
 ll f1(int x1,x2)
              ^
0_0_31553256_10986.cpp: In function 'long long int f1(int, int)':
0_0_31553256_10986.cpp:29:14: error: 'x2' was not declared in this scope
  for( i=4; i<x2-x1; i++)
              ^