#include<fstream>
using namespace std;
ifstream fin("factorial.in");
ofstream fout("factorial.out");
long long nnn,n,s,t,i,nn,ci;
int main()
{
    fin>>n;
    if(n==0)
    {
        fout<<1;
        return 0;
    }
    t=5;
    for(i=1;nn<n;i++)
    {
        nnn+=5; ci=i; s=0;
        while(ci%5==0)
            ci/=5,s++;
        nn+=s+1;
    }
    fout<<nnn;
    return 0;
}