#include <stdio.h>

long long n,p,ls,ld,s;

long nr(long n)
{
long n2,n5,i;

for(n2=0,i=2;i<=n;i*=2)
n2+=(n/i);
for(n5=0,i=5;i<=n;i*=5)
n5+=(n/i);
if (n2>n5) return n5;
      else return n2;
}

int main()
{
freopen("fact.in","rt",stdin);
freopen("fact.out","wt",stdout);

scanf("%lld",&p);

ls=1;
s=1;
ld=999999999;
while (ls<=ld)
{
n=(ls+ld)/2;
if (nr(n)>=p) {s=n;ls=n-1;}
else ld=n+1;
}

printf("%lld",s);
return 0;}