题解：SP25584 FCDC - Factorial Modulo

#include<bits/stdc++.h>
using namespace std;
#define N 10010
int count(int x,int shu)
{
    int cnt=0;
    while(x>0) x/=shu,cnt+=x;
    return cnt;
}
int solve(int a)
{
    if(a==1) return 1;
    int res=0;
    for(int i=2;i*i<=a;i++)
        if(a%i==0)
        {
            int cnt=0;
            while(a%i==0) cnt++,a/=i;
            int l=1,r=1e6,ans=0;
            while(l<=r)
            {
                int mid=l+r>>1;
                if(count(mid,i)>=cnt)
                    ans=mid,r=mid-1;
                else l=mid+1;
            }//二分
            res=max(res,ans);
        }
    res=max(res,a);//剩下的也要计算
    return res;
}
int n,m;
int main()
{
    cin>>n>>m;
    int ans=max(0,solve(m)-solve(n));
    cout<<ans;
}