#include <iostream>
#include <fstream>
#include <cstdio>
using namespace std;
FILE *fin,*fout;
long long n,p,i,x,k,s;
int main()
{
    fin=fopen("fact.in","r");
    fout=fopen("fact.out","w");
    fscanf(fin,"%lld",&p);
    if(p==0) {fprintf(fout,"1");return 0;}
    n=p*5;
    x=25;
    i=1;
    s=0;
    while(x<=n)
    {
        s+=n/x-i;
        i++;
        x*=5;
    }
    fprintf(fout,"%lld",(p-s)*5);
    return 0;
}