#include<iostream>
#include<fstream>
using namespace std;
ifstream fin("fact.in");
ofstream fout("fact.out");
int p;
int zeros(int x)
{
    int nr=0;
    int d_nr = 5;
    while(x >= d_nr)
    {
        nr+=x/d_nr;
        d_nr *= 5;
    }
    return nr;
}
int bs(int l,int r,int val)
{
    int min_nr = 1000000000;
    bool f = false;
    while(l <= r)
    {
        int mid = l+(r-l)/2;
        int z0 = zeros(mid);
        if(z0 == p) min_nr = min(min_nr,mid),f = true;
        if(p > z0) l=mid+1;
        else r=mid-1;
    }
    if(f) return min_nr;
    else return -1;
}
int main()
{
    fin>>p;
    if(p == 0) fout<<1;
    else fout<<bs(0,p*5,p);
}