#include <bits/stdc++.h>

using namespace std;
ifstream fin("fact.in");
ofstream fout("fact.out");
uint64_t P;
int main()
{
    fin>>P;
    uint64_t st=0,dr=0xffffffff;
    uint64_t mij = (st+dr)/2;
    while(st<dr)
    {
        mij=(st+dr)/2;
        uint64_t nr0 = 0;
        for(uint64_t i=5;i<mij;i*=5)
        {
            nr0+=mij/i;
        }
        if(nr0<P)
        {
            st=mij+1;
        }else
        {
            dr=mij-1;
        }
    }
    fout <<mij;
    return 0;
}