#include <iostream>
#include <fstream>

using namespace std;

int main()
{
    long long n,nract,numitor=5,suma=0;
    ifstream f("fact.in");
    ofstream g("fact.out");
    f>>n;
    nract=5;
    long long nr=1;
    if(n>0){
        while(suma<n){
            nract=nract+5;
            long long studiaza=nract;
            suma=0;
            numitor=5;
            while(studiaza/numitor>0){
                suma=suma+studiaza/numitor;
                numitor=numitor*5;
            }
            //cout<<suma;
            //nr++;
        }
        g<<suma;
    }
    else g<<1;
    return 0;
}

/*#include <iostream>
#include <fstream>

using namespace std;

int main()
{
    long long n,nract;
    ifstream f("fact.in");
    ofstream g("fact.out");
    f>>n;
    nract=5;
    long long nr=1;
    if(n>0){
        while(nr<n){
            nract=nract+5;
            long long studiaza=nract;
            while(studiaza%5==0){
                nr++;
                studiaza=studiaza/5;
            }
            //nr++;
        }
        g<<nract;
    }
    else g<<1;
    return 0;
}
*/