一本通1065

//qf
#include <bits/stdc++.h>
#define f(i,j,n) for(register int i=j;i<=n;i++)
using namespace std;
typedef long long ll;
inline ll read(){
    ll x=0;
    int f=1;
    char ch=getchar();
    while(!isdigit(ch)) {
        if(ch=='-') f=-1;
        ch=getchar();
    }
    while(isdigit(ch)) x=(x<<1)+(x<<3)+ch-48,ch=getchar();
    return x*f;
}
signed main(){
    int m=read(),n=read();
    ll s=0;
    f(i,m,n) if(i&1) s+=i;
    cout<<s<<endl;
    return 0;
}