#include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include using namespace std; typedef long long ll; #define LLMAX LLONG_MAX #define IMAX INT_MAX ll solve(ll r, ll c) { if (r != c) { if ((r*c)%2) { return r*(c/2)+(r+1)/2-1; }else { return (r*c)/2-1; } }else { if (r%2) { return 1+r*(r-1)-1; }else { return (r/2)*(r/2)-1; } } } int main() { ll r, c; cin >> r >> c; cout << solve(r, c) << endl; }