View Compilation Error

0_0_8542452_10150.cpp:6: error: `main' must return `int'
0_0_8542452_10150.cpp: In function `long long int sum(long int)':
0_0_8542452_10150.cpp:16: error: new declaration `long long int sum(long int)'
0_0_8542452_10150.cpp:3: error: ambiguates old declaration `unsigned int sum(long int)'