#include<iostream.h>   
#include<math.h>   
#include<fstream.h>   
  
ifstream f("fact.in");   
ofstream g("fact.out");   
  
int x,exmax,i,t,y;   
  
  
int putere(int x)   
{int a=5; int i=0;   
  
while(a<=x)   
{   
a*=5;   
i++;   
}   
return i+1;   
}   
  
int suma(int a, int b)   
{int s=0;   
 for(i=b;i>=1; i--)s+=(a/(pow(5,i)));   
  
return s;   
}   
  
  
  
int main()   
{ 
  
  
f>>x;y=5*x;t=0;   
while(t!=x)   
{exmax=putere(x);   
  
t=suma(y,exmax);   
y-=5;   
}   
if(x==0)g<<1; else  
g<<y+5;   
}