#include <iostream>
#include <fstream>
using namespace std;
ifstream in("fact.in");
ofstream out("fact.out");
int n,s,d,m,i,nr=0,f;
int main()
{

    in>>n;
    s=1;
    d=5*n+5;
    while(s<=d)
    {
        m=(s+d)/2;
        nr=0;
        for(i=5;i<=m;i=i*5)nr+=m/i;
        if(nr==n)f=m;
        if(nr<n)s=m+1;
        else d=m-1;
    }
    out<<f;
    return 0;
}