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

ifstream f("fact.in");
ofstream g("fact.out");
long long a,st,dr,n,m,p;
long long zero(long long n)
{
    long long x=0;
    while(n)
    {
        x=x+n/5;
        n=n/5;
    }
    return x;
}
int main()
{
f>>n;
st=1;
dr=pow(10,20);
while(st<=dr)
{
    m=(st+dr)/2;
    a=zero(m);
    if(a<n)
        st=m+1;
    else
    {
        if(n==a)
            p=m;
        dr=m-1;
    }
}
g<<p;
return 0;
}