#include<stdio.h>
using namespace std;
int desc(int a)
{


 int j,k,i;
    j=0;
   for(i=1;i<=a;i++)
   {
      k=i;
       while(k%5==0)
       {
          k=k/5;
           j++;
       }
   }
   return j;
}
int caut(int a,int b,int n)
{
    int m;

    if (b>a)
    {
        return -1;
    }
    else
    {
        m=(a+b)/2;
        if(desc(m)==n)
        {
            return m;
        }
        if(desc(m)<n)
        {
            a=m+1;
        return   caut(a,b,n);
        }
        else{

        b=m-1;
        return caut(a,b,n);
        }
    }
}
int main()
{
int p;

FILE *fp;
fp=fopen("fact.in","r");
fscanf(fp,"%d",&p);
long r,n,c;
c=0;
n=1000000000;
r=caut(c,n,p);
FILE *fw;
fw=fopen("fact.out","w");
fprintf(fw,"%ld",r);
fclose(fw);
fclose(fp);
}