#include <iostream>
#include <fstream>
using namespace std;
ifstream fin("fact.in");
ofstream fout("fact.out");

int fact0(int n)
{
	int nr=0,p=5;

    while(p<=n)
    {
        nr+=n/p;
        p*=5;
    }

    return nr;
}

int main()
{
    int p,n,st=0,dr=2000000000,k=-1;

    fin>>p;

    while(st<=dr)
    {
        n=(st+dr)/2;
        if(p==fact0(n))
            k=n;
        if(fact0(n)>=p)
            dr=n-1;
        else
            st=n+1;
    }

    if(k==0)
    fout<<1;

    else
    fout<<k;

}