/* -*- coding: utf-8 -*- * * 84.cc: No.84 悪の算盤 - yukicoder */ #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include using namespace std; /* constant */ /* typedef */ typedef long long ll; /* global variables */ /* subroutines */ /* main */ int main() { ll r, c; cin >> r >> c; ll ans; if ((r & 1) == 0 || (c & 1) == 0) ans = r * c / 2 - 1; else ans = r * c / 2; printf("%lld\n", ans); return 0; }