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#include <bits/stdc++.h>

using namespace std;
ifstream f("fact.in");
ofstream g("fact.out");
long long p,i,j;
int nr0(int x)
{   int nr5=0;
    for (int i=5;i<=x;i*=5)
    {   nr5+=x/i;
    }
    return nr5;
}
int main()
{
    f>>p;
    long long st=0,dr=2000000000,poz=-1,mid;
    //cout<<dr<<endl;
    while (st<=dr)
    {   mid=(st+dr)/2;
        int x=nr0(mid);
        if(x>p)dr=mid-1;
        else if (x<p)st=mid+1;
        else {poz=mid;dr=mid-1;}
        //cout<<mid<<' '<<x<<endl;
    }
    //cout<<endl<<poz;
    g<<poz<<'\n';
    return 0;
}