#include<fstream>
#define int long long
using namespace std;
ifstream fin("fact.in");
ofstream fout("fact.out");

int Cinci(int n){

int nr=0;

while(n && n%5==0){
    nr++;
    n/=5;
}

return nr;

}

int Nr_0_final(int n){

int s=0,i,c=5;

while(n > c){
    s+=n/c;
    c*=5;
}

return s;

}

int32_t main(){

int st,dr,mij,p,n,rez=-1,x;

fin>>p;

st=1;
dr = p*5;

while(st<=dr){

    mij=(st+dr)/2;

    x = Nr_0_final(mij);

    if(x >= p){
        rez=mij;
        dr=mij-1;
    }
    else
        st=mij+1;

}


fout<<rez;
}