#include <iostream>
#include<fstream>
using namespace std;
ifstream in("fact.in");
ofstream out("fact.out");
    int st,dr,x,p,mij;
    unsigned long long s;
int main()
{
    in>>p;
    st=1;
    dr=1000000000;
    while(st<dr)
    {
        mij=(st+dr)/2;
        x=mij;
        s=0;
        while(x)
        {
            s=s+x/5;
            x/=5;
        }
        if(s>=p)
            dr=mij;else st=mij+1;
    }
    out<<dr;
    return 0;
}