#include <bits/stdc++.h>
using namespace std;
#define el '\n'
#define ll long long
#define ld long double
#define ull unsigned long long
#define pll pair<long long, long long>
#define ppll pair< pair<long long, long long>, long long >
#define ff first
#define ss second
#define pb push_back
#define pf push_front
#define all(x) x.begin(), x.end()
const ll DIM = 2e5 + 7;
const ll INF = 1e18;
const ll mod = 1e9 + 7;
const ll maxlog = 20;
void solve() {
ll n, m;
cin >> n >> m;
ll ans = 0;
for (int j=1; j<=m; j++) {
char ch;
cin >> ch;
if (ch == 'N') ans += 1;
else if (ch == 'W') ans += 2;
else if (ch == 'S') ans += 3;
else if (ch == 'X' && j != m) ans = -INF;
}
if (ans < 0) cout << -1 << el;
else cout << ans << el;
}
signed main(){
ios::sync_with_stdio(false);cin.tie(nullptr);cout.tie(nullptr);
//freopen("nocross.in", "r", stdin);
//freopen("nocross.out", "w", stdout);
int ntest = 1;
//cin >> ntest;
while (ntest--){
solve();
}
return 0;
}
;
