#include <iostream>
#include <fstream>
using namespace std;

int zerouri(int k){
    int nr=0,f=5;
    while(k/f>0){
        nr+=k/f;
        f=f*5;
    }
    return nr;
}
int main()
{     int p,stanga=1,dreapta,mijloc;
    ifstream a("fact.in");
    ofstream b("fact.out");
    a>>p;
    dreapta=p*5;
    while(stanga<=dreapta)

        {mijloc=(stanga+dreapta)/2;
        if(zerouri(mijloc)<p)
            stanga=mijloc+1;
        else
            dreapta=mijloc-1;}

    if(zerouri(stanga)==p)
        b<<stanga;
      else
        b<<dreapta;

        return 0 ;
}