#include<cstdio> 
const int N=1<<15; 
long long p; 
long long zero (long long n) 
{  
int s=0; 
while (n) 
{     
s=s+n/5;     
n=n/5; 
} 
return s; 
}   
long long fact(int p) 
{     
int i,pas=N;     
for ( i=0;pas!=1;pas=pas/2)    
if (zero(i+pas)<p)         
i=i+pas; 
return (i+1); 
} 
int main() 
{ 
freopen("fact.in","r",stdin); 
freopen("fact.out","w",stdout); 
scanf("%lld",&p); 
long long  k=fact(p); 
printf("%lld",k); 
return 0; 
}