#include<iostream>
#include<fstream>
using namespace std;
int zero(int n)
{
    int ans=0;
    while(n>=5){
        ans+=n/5;
    n/=5;
    }
    return ans;
}
int cautare(int p)
{
    int st=1;
    long long dr=200000005;
    while(st<dr)
    {
        int mij=(st+dr)/2;
        if(zero(mij)==p)
            return mij-mij%5;
        else if(zero(mij)>p)
            dr=mij-1;
        else
         st=mij+1;
    }
}
int main()
{
    ifstream cin("fact.in");
    ofstream cout("fact.out");
 int p;
 cin>>p;
 cout<<cautare(p);
}