Rodovia

#include <bits/stdc++.h>
using namespace std;
const int MAX = 500005;

int n;
vector<int> G[MAX], G_t[MAX];
stack<int> S;
int cor[MAX];

void preenche(int v) {
    cor[v] = 1;
    for(int &w : G[v])
        if(!cor[w])
            preenche(w);
    S.push(v);
}

void dfs(int v) {
    cor[v] = 1;
    for(int &w : G_t[v])
        if(!cor[w])
            dfs(w);
}

bool kosaraju() {
    for(int i = 0; i < n; i++)
        if(!cor[i])
            preenche(i);
    memset(cor, 0, sizeof(cor));
    int sz = 0;
    while(!S.empty()) {
        int u = S.top();
        S.pop();
        if(cor[u]) continue;
        dfs(u);
        sz++;
    }
    return sz == 1;
}

int32_t main() {
    cin >> n;

    for(int i = 0; i < n; i++) {
        int a, b;
        cin >> a >> b; a--; b--;
        G[a].push_back(b);
        G_t[b].push_back(a);
    }
    if(kosaraju()) cout << "S\n";
    else cout << "N\n";

    return 0;
}