#include<stdio.h>
long n,i;
long long k;
long zero(long k)
{
		long i=5;
		long long num=0;
		while(i<=k)
			{
				num+=k/i;
				i*=5;
			}
		return num;
}



int main()
{
		freopen("fact.in","r",stdin);
		freopen("fact.out","w",stdout);
		scanf("%ld",&n);
		for(i=1;i<=1000000000;++i)
			{
				k=zero(i);
				if(k==n)
					{
						printf("%lld\n",i);
						return 0;
					}
			}
		return 0;
}