Compilare: main.cpp: In function 'int main()': main.cpp:38:40: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)', declared with attribute warn_unused_result [-Wunused-result] freopen ("trapez.in" , "r" , stdin); ^ main.cpp:39:42: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)', declared with attribute warn_unused_result [-Wunused-result] freopen ("trapez.out" , "w" , stdout); ^ main.cpp:41:22: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result] scanf ("%d" , &n); ^ main.cpp:44:37: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result] scanf ("%lld%lld" , &a , &b); ^ main.cpp:72:32: warning: 'lg' may be used uninitialized in this function [-Wmaybe-uninitialized] ans = ans + 1LL * lg * (lg - 1) / 2LL; ~~~~^~~~