2657: 考试秘籍

include <bits/stdc++.h>

using namespace std;
long long a, b, sum;
int main()
{
cin >> a >> b;
if (a%20)
a/=2;
else
a=a/2+1;
if (b%20)
b/=2;
else
b=b/2+1;
sum+=b-a+1;
cout << sum;
}

反思：要运用好公式