#include <iostream>
#include <fstream>
#define nmax 1000000
using namespace std;

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

long long p;
long nr;
long rez;
long v[nmax+1];

void fact()
{
    int j;
    for(int i=5;i<=nmax;i+=5)
    {
        j=i;
        while(j%5==0 && j)j/=5,v[i]++;
        v[i]+=v[i-1];
        v[i+1]=v[i+2]=v[i+3]=v[i+4]=v[i];
    }
}

int main()
{
    f>>p;
    fact();
    if(p==0){g<<1;return 0;}

    long st=1, dr=nmax, c;

    while(st<=dr)
    {
        c=(st+dr)/2;
        nr=v[c];

        if(nr==p)
        {
            rez=c;
            dr=c-1;
        }
        else if(nr>p)dr=c-1;
        else st=c+1;
    }
    if(rez==0)g<<rez-1;
    else g<<rez;
    return 0;
}