#include<stdio.h>
using namespace std;
FILE*in=fopen("factorial.in","rt");
FILE*out=fopen("factorial.out","wt");
int s=1,i=1,p,rezultat,q ;
int main()
{
fscanf(in,"%d",&p);
    while(rezultat!=p)
    {
    if((s*i)%10==0)
        {
            rezultat++;
            s=s*i/10;
        }
    else
    s=(s*i)%10;
    i++;
    }
    q=i-1;

fprintf(out,"%d",q);

fclose(out);
fclose(in);
return 0;
}