#include<bits/stdc++.h>
using namespace std;

int main(){
    int N; cin >> N;
    string s; cin >> s;
    int ans=0;
    int j=0;
    for(int i=0;i<N;i++){
        if(s[i]=='3'||s[i]=='5'||s[i]=='7'){
            ans++;
        }else{
            if(j!=0){
                if(s[j]=='1'&&s[i]=='1') ans++;
                if(s[j]=='1'&&s[i]=='9') ans++;
                if(s[j]=='9'&&s[i]=='1') ans++;
                j=0;
            }else{
                j=i;
            }
        }
    }
    cout << ans << endl;
}