i am taking my first C++ class and i can not clear the following error can anyone help

error C2447: '{' : missing function header (old-style formal list?)

//christine gershen

// Exercise 4.17: Encryption.cpp

// Encrypts data given by user.

#include <iostream> // required to perform C++ stream I/O

#include <iomanip> // required to perform setprecision stream manipulator

using namespace std; // for accessing C++ Standard Library members

int main(); // function main begins program execution

{

int main=0;

int digit_one; //store digit one

int digit_two; //store digit two

int digit_three; //store digit three

int digit_four; //store digit four

cout <<"Enter four-digit number:"; //asking the user to enter four-digit number

cin >> main; //four-digit number

digit_one=main%10; // digit_one is first four-digit number

digit_two=main/10%10; // digit_two is second four-digit number

digit_three=main/100%10; //digit_three is third four-digit number

digit_four=main/1000%10; //digit_four is fourth four-digit number

digit_one=(digit_one + 7%10); //add digit_one to 7 and mod 10

digit_two=(digit_two + 7%10); //add digit_two to 7 and mod 10

digit_three=(digit_three + 7%10); //add digit_three to 7 and mod 10

digit_four=(digit_four + 7%10); //add digit_four to 7 and mod 10

cout <<"Encrypted digits:"; << digit_three; digit_four; digit_one; digit_two; << endl;// display encrypted numbers

return 0; // indicate that program ended successfully

}; // end function main

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