#include <fstream>
using namespace std;
int main()
{int N,P,k,i,t;
ifstream f("fact.in");
ofstream g("fact.out");
f>>P;
N=0;
for(i=1;i<=P;i++)
{N=N+5;
}
if(P!=0){}
t=N;
k=-1;
while(t/5>1) {
t=t/5;
k=k+1;}
N=N-5*k;
g<<N;
return 0;

}