#include <bits/stdc++.h>

using namespace std;
ifstream fin("fact.in");
ofstream fout("fact.out");
//functie care returneaza numarul de zero-uri
int nrzero(int n)
{
    int k = 0;
    while (n >= 5)
    {
        k = k + n / 5;
        n = n / 5;
    }
    return k;
}

int main()
{
    int p,mij,st=0,dr=INT_MAX,k=-1;

    fin>>p;
    //caut binar primul n care are suficienti de 0
    while(st<=dr)
    {
        mij=(st+dr)/2;
        if(p==nrzero(mij))
            k=mij;
        if(nrzero(mij)>=p)
            dr=mij-1;
        else
            st=mij+1;
    }

    if(k==0)
        fout<<1;
    else
        fout<<k;
    return 0;
}