#include <fstream>
using namespace std;
ifstream f("fact.in");
ofstream g("fact.out");
long long p;
inline int Count(int n){

    int cnt=0;
    while(n)
    {
        cnt+=n/5;
        n/=5;
    }
    return cnt;
}
inline void Search(){

    int st=1,dr=100000000000,m,ans=-1;
    while(st<=dr)
    {
        m=(st+dr)/2;
        if(Count(m)>=p)
        {
            dr=m-1;
            ans=m;
        }
        else
            st=m+1;
    }
    g<<ans;
}
int main()
{
    f>>p;
    Search();
    return 0;
}