#include <stdio.h>
#include <stdlib.h>

int main()
{   FILE *f,*g;
    f=fopen("fact.in","r");
    g=fopen("fact.out","w");
    long long  P,n=1,S=0;
    fscanf(f,"%lld",&P);
    if(P==0)
    fprintf(g,"%lld",n);
    else{

    while(S<P)
    {
        long long p=5;
        S=0;
        while(n/p)
        {S+=n/p;
         p=p*5;}
         n++;
    }
    n=n-1;
    fprintf(g,"%lld",n);
    }


    return 0;
}