#include <iostream>
#include <fstream>
using namespace std;
ifstream fin("fact.in");
ofstream fout("fact.out");
long long p,n;
int zero(long long q)
{
    long long sum=0,p=5;
    while(p<=q)
    {
        sum+=(q/p);
        p*=5;
    }
    return sum;

}
long long cautare(long long st,long long dr)
{long long mj,nr0;
if(st<=dr)
{
    mj=(st+dr)/2;
    nr0=zero(mj);
    if(nr0<p)return cautare(mj+1,dr);
    if(nr0>p) return cautare(st,mj-1);
    return mj-(mj%5);
    }
 return -1;
}
int main()
{fin>>p;
    if(p==0)
        fout<<1;
    else{
    n=cautare(1,1000000000);
    fout<<n;
    }
    return 0;

}