#include<iostream>

using namespace std;

int main(){

int a,b,c;

cin>>a>>b;

for(int i=a;i<=b;i++){

if(a>b) {

cout<<0<<endl;

break;

}

if(i%2!=0){

c+=i;

}

}

cout<<c<<endl;

return 0;

}

//Theo