#include <iostream>
#include <fstream>
#include <cmath>
 
using namespace std;
 
int nrzerouri(int k){
    if(k>0)
        return 5*nrzerouri(k-1) + 1;
    return 1;
}
 
int main(){
    ifstream f("fact.in");
    int P, nr=0;
    f>>P;
    f.close();
 
    int sum=0;
    while(P>0){
 //cout<<"P="<<P<<"\n";
            int y=(log((double)P)/log(5.0));
            int x= nrzerouri(y);
			//cout<<"x="<<x<<"\n";
            sum += (int)(P/x) * pow(5,y);
			if(x>P)
				break;
            P= P%x;
		//cout<<"new P="<<P<<"\n";
            }
 
 
    ofstream g("fact.out");
    if(sum==0)
        g<<1;
    else g<<sum*5;
    g.close();
 
    return 0;
}