#include <fstream>

using namespace std;
    int p,c,f,ff,stillgoing,nr;
int main()
{
    ifstream fin("fact.in");
    ofstream fout("fact.out");
    fin >> p;c=2;f=1;
    stillgoing=1;
    while (stillgoing)
    {
    if (p==0){f=1;break;}
    f*=c;
    c++;
    ff=f;
    while (ff%10==0){ff/=10;nr++;}
    if (nr==p)break;
    nr=0;
    }
    fout << c-1;

    fin.close();
    fout.close();
    return 0;
}