#include<fstream>
using namespace std;

int main(){
    unsigned long P;
    unsigned long long N=1, k=1;
    ifstream in;
    in.open("fact.in");
    in>>P;
    in.close();
    if(P>0)
    {
        for(long i=0;i<P;i++)
        {
            k*=5;
        }
    }
    else
    {
        k=1;
    }
    unsigned short i=0;
    while(N%k!=0)
    {
        i+=5;
        N*=i;
    }
    ofstream out;
    out.open("fact.out");
    out<<i;
    out.close();
}