#include <iostream>
#include <fstream>
#include <algorithm>
using namespace std;
ifstream f("fact.in");
ofstream g("fact.out");
long long ok(long long n)
{   if(n<5) return 0;
    long long d=5;
    long long nrap=0;
    while(d<=n)
    {   nrap+=n/d;
        d*=5;
    }
    return nrap;
}
int main()
{   int p;
    f>>p;
    long long sol=0,st=1,dr=99999999999999999;
    //g<<dr<<'\n';
    while(st<=dr)
    {   long long mij=(st+dr)/2;
        if(p<=ok(mij))
        {   sol=mij;
            dr=mij-1;
        }
        else st=mij+1;
        //g<<mij<<'\n';
    }
    g<<sol;
}