include<bits/stdc++.h>

using namespace std; int main(){

int i,s = 0,a,b,c,d;
cin>>a>>b;
if(a % 2 == 0){
	c = a + 1;
}else{
	c = a;
}
if(b % 2 == 0){
	d = b - 1;
}else{
	d = b;
}
for(i = c;i <= d;i+=2){
	s = s + i;
}
cout<<s<<endl; 

}