//#include<iostream>
#include<fstream>
using namespace std;
int P,s=0;
ifstream cin("fact.in");
ofstream cout("fact.out");
long long exp(int k);
long long cautb(int x)
{
    long long st=1;
    long long dr=200000000;
    long long ret;
    while(st<=dr)
    {
        long long mij=(st+dr)/2;
        if(exp(mij)<P)
            st=mij+1;
        else if(exp(mij)>=P)
        {
            ret=mij;
            dr=mij-1;
        }
    }
    return ret;
}

long long exp(int k)
{
    long long x=1;
    long long y=0;
    while(x<=k)
    {
        x=x*5;
        y=y+k/x;
    }
    return y;
}

int main()
{
    cin>>P;
    cout<<cautb(P);
    return 0;
}