[백준 2004] 조합 0의 개수 (Math) (C/C++) (★)

#include <stdio.h>
#include <iostream>
#include <algorithm>
#include <string>
#include <vector>
#include <math.h>
using namespace std;
 
long long N, M;
 
long long twoN;
long long twoM;
long long twoNM;
 
long long fiveN; 
long long fiveM;
long long fiveNM;
 
int main(void)
{
//    freopen("B2004_input.txt", "r", stdin);
    
    cin >> N >> M;
    
    for(long long i = 2; i <= N; i *= 2)
    {
        twoN += N / i;
    }
    for(long long i = 2; i <= M; i *= 2)
    {
        twoM += M / i;
    }
    for(long long i = 2; i <= N-M; i *= 2)
    {
        twoNM += (N-M) / i;
    }
    
    for(long long i = 5; i <= N; i *= 5)
    {
        fiveN += N / i;
    }
    for(long long i = 5; i <= M; i *= 5)
    {
        fiveM += M / i;
    }
    for(long long i = 5; i <= N; i *= 5)
    {
        fiveNM += (N-M) / i;
    }
    
    cout << min(twoN-twoM-twoNM, fiveN-fiveM-fiveNM);
    
    return 0;
}