#include <fstream>

using namespace std;

int zero(int x)
{
    long long k=0;
    for(int i=5; i<=x; i*=5) k=k+x/i;

    return k;
}

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

    int p;
    fin>>p;

    if(p==0) fout<<"1";
    else
    {
        int lo=1, hi=1000000000, mid;
        while(lo<=hi)
        {
            mid=lo+(hi-lo)/2;
            if(zero(mid)<p) lo=mid+1;
            else hi=mid-1;
        }
        mid=lo+(hi-lo)/2;
        if(zero(mid)>p) mid--;
        if(zero(mid)==p) fout<<mid;
        else fout<<"-1";
    }
}