朴素 $\Theta (n)$加玄学卡常就能过……

上代码：

#include <bits/stdc++.h>
#define int long long
using namespace std;

signed main()
{
    int n,l,r;
    cin >> n >> l >> r;
    int maxn=-1;
    for (register int i=r-l>100000000?r-100000000+1:l;i<=r;i++)
    {
        maxn=max(maxn,i%n);
    }
    cout << maxn << endl;
    return 0;
}