#include <iostream>
#include <fstream>
using namespace std;
ifstream fin("fact.in");
ofstream fout("fact.out");
int numar(int n)
{int cnt=0;
for(int i=5;i<=n;i=i*5)
cnt=cnt+n/i;
return cnt;
}
int main()
{int n,cnt=0,p,x=0;
fin>>p;
int i=1;
if(p==0) cout<<"1";
else { while(x!=p)
{x=numar(i);
i++;
}
fout<<i-1;}
fin.close();
fout.close();
    return 0;
}