#include <cstdio>

using namespace std;

int n,st,dr,s,i,mid;

int main()
{
    freopen("fact.in", "r", stdin);
    freopen("fact.out", "w", stdout);
    scanf("%d",&n);
    st=1;dr=500000000;
    while(st<=dr)
    {
        mid=(st+dr)/2;
        s=0;
        for(i=5;i<=mid;i*=5) s+=mid/i;
        if(s>=n) dr=mid-1;
        else st=mid+1;
    }
    printf("%d",st);
    return 0;
}