https://www.acmicpc.net/problem/1676
#include <iostream>
using namespace std;
int get_num_cnt(int num, int N) // num is 2 or 5
{
int cnt = 0;
while (1)
{
if (N % num == 0)
{
cnt++;
N /= num;
}
else
{
break;
}
}
return cnt;
}
int main(void)
{
int N, cnt2 = 0, cnt5 = 0;
cin >> N;
for (int i = N; i >= 1; i--)
{
cnt2 += get_num_cnt(2, i);
cnt5 += get_num_cnt(5, i);
}
cout << min(cnt2, cnt5);
return 0;
}