#include using namespace std; typedef long long ll; #define rep(i,n) for(i=0;i>r >>c; ll ans; if(r!=c){ if(r%2==0 || c%2==0) ans=r*c/2-1; else ans=r*c/2; } else{ ans=((r+1)/2)*((c+1)/2)-1; } std::cout << ans << std::endl; return 0; }