#include<iostream>
#include<fstream>
#include<time.h>
using namespace std;

int p,c,k,r,n;

int main()
{int t1,t2;
t1=clock();
ifstream g("fact.in");
g>>p;
r=p;
while(r>5)
{k++;
 c+=(r/5)*k;
 r/=5;}
ofstream t("fact.out");
n=p*5-c*5+5;
t<<n;
t.close();
g.close();
t2=clock();
cout<<(double)(t2-t1)/CLOCKS_PER_SEC;
return 0;}