#include <iostream>
#include <cmath>
#include <fstream>
 using namespace std; 
ifstream f ("fact.in");
ofstream g ("fact.out");
int m,p,logaritm; 
void zero(int);


int main ()
{ 
f>>p;
logaritm=log10(p)/log10(5); m=logaritm*5; 
if (logaritm==0) logaritm=1;
zero (p*5);

}

void zero(int p1)
{ int mem,k=0,suma=0;mem=p1;
do
{  k=0;suma=0; 
do
{
p1=p1/5; suma+=p1; k++;
} while  (k-1!=logaritm);
mem-=5;p1=mem;
}
while (suma!=p);
g<<p1+5<<endl;
}