#define _USE_MATH_DEFINES
#include  <cmath>
#include <cstdio>
#include <vector>
#include <iostream>
#include <algorithm>
#include <string>
#include<math.h>
#include<iomanip>
#include<stdio.h>
#include <stdlib.h>
#include<stdio.h>
#include <queue>
#include<map>
#include <fstream>
#include <sstream>
#include<set>
#include<stack>
#include<time.h>
#include <sys/types.h>
#include <tuple>
#include <numeric>
#include <iterator>

typedef long long int ll;
//#include<bits/stdc++.h>


using namespace std;

ll gcd(ll a, ll b) {
    if (a < b)swap(a, b);
    if (b == 0)return a;
    return gcd(b, a % b);
}
int lcm(int a, int b) {
    return a * b / gcd(a, b);
}




int main()
{

    int Q;
    Q = 1;
    //cin >> Q;   

    while (Q--) {
        ll a = 0;
        string p;
        cin >> p;
        int x=0, y = 0;
        for (int i = 0; i < p.size() ; i++) {
            if (p[i] == 'p') {
                x = 1, y = 1;
            }
            if (p[i] == 'o') {
                if (x == 1)x = 2;
                else x = 0;
                y = 0;
            }
            if (p[i] == 'n') {
                if (x == 2) {
                    x = 0; a++;
                }
                else x = 0;
                if (y == 3) {
                    if (a < 2)a = -1;
                    else a -= 1;
                    cout << a;
                    return 0;
                }
                else y = 0;
            }
            
            if (p[i] == 'a') {
                if (y == 1) {
                    y = 2;
                }
                else y = 0;
                x = 0;
            }
            if (p[i] == 'i') {
                if (y == 2) {
                    y = 3;
                }
                else y = 0;
                x = 0;
            }
            
        }
        cout << -1;
    }
        return 0;
}