#include<iostream>
#include<fstream>
using namespace std;
ifstream f("fact.in");
ofstream g("fact.out");
unsigned int OK,i,j,l=0,p,d;
long long t;
int main(){
    f>>p;
   i=1;
   OK=1;
   while(OK!=0){
        t=1;
        l=0;
        for(j=1;j<=i;j++)
            t=t*j;
        if(t%10==0){
                while(t%10==0){
                        l++;
                t=t/10;}
                if(l==p)
                {
                d=i;
                OK=0;
                }}
              i++;}
              g<<d;
              return 0;}