#include<fstream>
#include<math.h>
using namespace std;
int caut_fact(int x)
{
    unsigned long long i,s=0,st=0,dr=5*pow(10,8);
    while(st<=dr){
        int mid=(st+dr)/2;
     for(i=12;i>=1;--i)
    {
        s=s+mid/pow(5,i);
    }
    if(x<=s)
    {
        dr=mid-1;
    }
    else
    {
        st=mid+1;
    }
    s=0;
    }

    return st;
}
int main()
{
    ifstream fin ("fact.in");
    ofstream fout ("fact.out");
    unsigned long long x;
    fin>>x;
    fout<<caut_fact(x);
}