#include <fstream>

using namespace std;

ifstream fin("fact.in");
ofstream fout("fact.out");

long n;

int fact(long n)
{
    int r=0;
    while (n>=5) {
        r+=n/5;
        n/=5;
    }
    return r;
}

int caut_bin()
{
    int pas=1<<23;
    int i=0;
    while (pas!=0) {
        if (fact(i+pas)<n) i+=pas;
        pas/=2;
    }
    return i+1;
}

int main()
{
    fin>>n;
    if (n==0) fout<<1;
    else fout<<caut_bin();
}