#include<bits/stdc++.h> using namespace std; int b[100],n,max1=0,a=0,i,j; int main(){ cin>>n; b[1]=1; for(i=2;i<=n;i++){ if(b[i]==0){ for(j=i+i;j<=n;j+=i) b[j]=1; } } for(i=4;i<=n;i++){ if(b[i]==1) a++; if(b[i]==0) a=0; if(a>max1) max1=a; } cout<<max1<<endl; return 0; }