#include <fstream>

using namespace std;

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

long z;
long n;

int zeroes(long n)
{
    long long power=5;
    int result=0;
    int add;
    while(add=int(n/power))
    {
        result+=add;
        power=power*5;
    }
    return result;
}

void binsearch(long a,long b)
{
    long c=a+b/2;
    long aux=zeroes(c);
    if(a<b)
    {
        if(aux>z)
        {
            binsearch(a,c);
        }
        else if(aux<z)
        {
            binsearch(c,b);
        }
        else n=c;
    }
}

int main()
{
    f>>z;
    binsearch(0,400000020);
    g<<n/5*5;
    return 0;
}