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

ifstream f("fact.in");
ofstream g("fact.out");

int v[200000000];
const int NMAX=200000000;

int cautbin(int x)
{
    if(x==0) return 1;
    int stanga=1,dreapta=NMAX,m;
    while(stanga<=dreapta)
    {
        m=(stanga+dreapta)/2;
        if(v[m]==x)
            return m;
        else if(v[m]<x) stanga=m+1;
        else dreapta=m-1;
    }
    return -1;
}

int main()
{
    int i,j,p,temp;
    for(i=1;i<=NMAX;i++)
    {
    v[i]=v[i-1]+1;
    temp=i;
    while(temp%5==0)
    {
        v[i]++;
        temp/=5;
    }
    }
    f>>p;
    g<<cautbin(p)*5;

    f.close();
    g.close();
    return 0;
}